Update built-in topic tree

Test Plan:
- None
Adjust storage API

Test Plan:
- Tested out the APIs manually (hard to test for now with automated.
  because the storage APIs are not available to a browser).
Add isFirefoxOS check and use storage for topic tree

Test Plan:
- Tested the API manually
Use domain colors for titles and headers, use title in header, add Back to header, add Search.

Test Plan:
- Basic manual testing.