feat(simple redux): implement simple redux helpers to register and remove reducers

affects: @patternfly/simple-redux

Author: karelhala

package-lock.json

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+# CREDITS
+
+* Based on a proposal for adding reducers on the fly by [Vojtech Szocs](https://github.com/vojtechszocs)
+
+* Initially used in [ManageIQ project](http://manageiq.org/)
+
+* Man code written by [Vojtech Szocs](https://github.com/vojtechszocs) and [Karel Hala](https://github.com/karelhala)

packages/simple-redux/CREDITS.md

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+### @patternfly/simple-redux
+This package provides couple of helper functions which helps you to write redux reducers and most importantly it allows
+you to add reducers on the fly.
+
+All credit goes to @vojtechszocs proposing this behavior and how it should work.
+#### General Usage
+To use this package simply install it, add some reducers and create redux store from `rootReducer`.
+
+1. Install it
+```bash
+> npm install --save @patternfly/simple-redux
+```
+
+2. Add some reducers
+```javascript 1.8
+import { addReducer } from '@patternfly/simple-redux';
+
+addReducer((state, action) => { ...state });
+```
+
+3. Import rootReducer and use it as one of your reducers
+```javascript 1.8
+import { createStore, applyMiddleware } from 'redux';
+import { rootReducer, middlewares } from '@patternfly/simple-redux';
+
+const store = createStore(rootReducer, {}, applyMiddleware(...middlewares));
+```
+
+#### Complex usage
+You are free to use `rootReducer` as you wish, just bear in mind that only reducers registered via `addReducer` can be
+ removed on the fly.
+
+##### With combine reducers
+If you want to use combineReducers function from redux there is helper method which helps you combine current state 
+with state from combine reducers `combineReducersWithState`. What it does is that it takes state ane join it together 
+with state from `combineReducers` function. 
+```javascript 1.8
+import { combineReducersWithState } from '@patternfly/simple-redux';
+import { someReducer } from './reducers';
+
+addReducer(combineReducersWithState({
+  someValue: someReducer
+}))
+```
+
+##### With redux browser extension
+To enable browser extension for redux monitoring simply follow same logic as before with composeEnhancers, plus use 
+rootReducer from simple redux library as reducer combination.
+```javascript 1.8
+import { createStore, applyMiddleware, compose } from 'redux';
+import { rootReducer, middlewares } from '@patternfly/simple-redux';
+
+const composeEnhancers = window.__REDUX_DEVTOOLS_EXTENSION_COMPOSE__ || compose;
+
+const store = createStore(
+    rootReducer,
+    {},
+    composeEnhancers(applyMiddleware(...middlewares))
+  );
+```
+
+#### Helper functions
+This library comes bundled with some helper functions to make it easier for you to maintain regular redux, adding 
+reducers and to make it easier to create reducer from Object.
+##### addReducer
+Basic function used to add new reducer to reducers list. It takes one argument callback function, which will be called
+with state and action from redux.
+* callback - reducer function callback
+  * state - redux state to call with callback function
+  * action - which action was triggered
+  
+You then can remove these reducers from reducers list at any time, by calling callbacks returned frum `addReducer` 
+function.
+```javascript 1.8
+//add new reucer
+import { reducerFunction } from './yourRedeucers';
+import { addReducer } from '@patternfly/simple-redux';
+
+const reducerRemove = addReducer(reducerFunction);
+const reducerRemove2 = addReducer((state, action) => reducerFunction(state, action));
+
+//remove these reducers
+reducerRemove();
+reducerRemove2();
+```
+
+##### rootReducer
+Reducer with reducers list, this object holds all active reducers and calls them whenever new actin is triggered. Use
+this object to create new store.
+```javascript 1.8
+import { createStore } from 'redux';
+import { rootReducer } from '@patternfly/simple-redux';
+
+createStore(rootReducer);
+```
+
+##### applyReducerHash
+This function will help you to construct reducers out of object. Alternative to using switch statements in redux.
+```javascript 1.8
+import { applyReducerHash, addReducer } from '@patternfly/simple-redux';
+import { ACTION_ONE, ACTION_TWO } from './yourActionTypes'; 
+
+//simple reducer function
+function firstReducer(state, action) {
+  return {
+    ...state,
+    someData: action.payload.someData
+  };
+}
+
+//map reducer functions to action type keys
+const reducersHash = {
+  [ACTION_ONE]: firstReducer,
+  [ACTION_TWO]: (state, action) => ({
+    ...state,
+    anotherData: action.payload.anotherdata
+  }),
+  'actionThree': (state = {}) => ({...state})
+};
+
+//create reducer with applyReducerHash and add it to reducers list
+addReducer((state, action) => applyReducerHash(reducersHash, state, action));
+```
+
+##### middlewares
+There is log reducer active if you are in development mode `process.env.NODE_ENV` is set to `development` so to add any
+new middlewares, just push them to `middlewares` array and create store with these middlewares.
+```javascript 1.8
+import { createStore } from 'redux';
+import { middlewares, rootReducer } from '@patternfly/simple-redux';
+import ReduxThunk from 'redux-thunk';
+
+middlewares.push(ReduxThunk);
+const store = createStore(
+  rootReducer,
+  applyMiddleware(...middlewares)
+);
+```
+
+#### Contribution
+
+1. Fork this repository
+
+2. Pull your fork
+```bash
+> git pull git@github.com:${YOUR_NAME}/patternfly-react.git
+```
+
+3. Set up remote
+```bash
+> git remote add upstream https://github.com/patternfly/patternfly-react.git
+```
+
+4. Install depenencies
+```bash
+yarn install
+```
+
+5. Run storybook
+````bash
+yarn start
+````
+
+6. Make some changes and create Pull request