Add wasm compatible database using gloo_storage::LocalStorage

[benthecarman]

Description

Closes #450

Adds a new database type for wasm builds. This is basically copied from MutinyWallet/mutiny-node#5

Notes to the reviewers

I am not sure if the tests are working correctly, couldnt figure out how to properly run with them without wasm-pack

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

[notmandatory]

@futurepaul sorry for the delay in commenting on this PR, it looks like a great addition but right now we're trying to avoid adding new features like this to bdk until we know how it will fit in with the bdk_core release 1.0 refactoring that the team is focused on. Rather than wait for that to shake out, since you're only implementing a bdk public trait how would you feel about making a little repo for this in your account? That way anyone who wants to try it out can easily add it as a dependency and you'll be able to iterate quickly on improvements. Then in a few months once the new bdk 1.0 APIs are solidified we can revisit pulling this into the bitcoindevkit org.