Investigate Tree View Component

[clarkbw]

Investigate and review the various Tree View components available as modules compared to the internal Firefox Tree View module available.  This module will be the basis for the Source Code Tree View.

[gregtatum]

For my reference, existing Firefox Tree View components:
fitzgen's: https://github.com/mozilla/gecko-dev/blob/master/devtools/client/shared/components/tree.js
honza's: https://github.com/mozilla/gecko-dev/tree/master/devtools/client/shared/components/tree

[clarkbw]

@TatumCreative make sure to take a look at the comments by @markerikson in https://github.com/jlongster/debugger.html/issues/104#issuecomment-216732509

[jlongster]

Let's merge this with #104. We've done the investigation, now we just need to tie it back to the sources view.

@TatumCreative I'll ping you tomorrow because I should have a basic sources tree working with Nick's tree view then. We should compare notes.