Add StyleBundle classes + injection methods to CommunicationBridge

- Moved all bridge functionality to .bridge package
- Remove hard-coded css <link> tags in HTML
- Add class that lets us load assets/ packaged CSS

This should make it easy to load CSS from other parts of the
filesystem later on, and also switch between them easily.

Change-Id: I4d3699adf9318427bc35feb65db69e6ab5d9175f
Merge "Add StyleBundle classes + injection methods to CommunicationBridge"