Two minor improvements - findByTag and hidden type support like android

[stonyw]

I like CSLinearLayoutView very much. It is difficult to arrange the views in iOS without it.

I have two ideas to make life easier.

1. add findByTag for and let the CSLinearLayoutItem share same tag value with its view.
   stonyw@a177cb4
   stonyw@41656a5
   I saw CSLinearLayoutItem did have tag and didn't use it yet. I added findByTag first. I find it is hard to maintain two tag id lists if I use tag. It is better to share the same tag id list.
2. add hidden support.
   stonyw@09d8b9c
   Hidden has two meanings in Android: Invisible and Gone. I want to hide some views in CSLinearLayout and show them again later. "Gone" is useful to me.
3. The rest commits are for ARC. @jaydee3 has a pending pull request Various improvements + Adding shortcuts for labels & images #2 .