Implement a JS <-> Java bridge.

- Two way message sending and receiving on both JS & Java ends.
- Bridge makes sure that events are fired onLoad.
- Loads pages by injecting data via JS into an empty HTML page, than
  just injecting HTML directly into the WebView.
- Set <base> URL in the base HTML page so that images load
- Load only the lead sections of articles (for now!)
- Default page html & js loaded from disk (assets)

Change-Id: Ie189816d2a9f68c3a750b175d06695e0f970c42c