Fix EVERYTHING! Part 3

This pull request is about making the actual browser extensions work again!
- Chrome 'works'! At least, app and Extension load and communicate together, and the new polymer UI shows up in the extension, and works as far as it's been implemented so far.
- Firefox build rules are restored, but I'll need some help to get the .xpi to actually work. cc @salomegeo :grinning:
- There are some errors in the new `freedom-for-chrome-for-uproxy`, some related to the socks-rtc stuff, some not, which need to be resolved in the next pull request(s).
- Removed all trace of sass, as well as some completely unused npm modules and bower components.

Tested: Jasmine & manual UI inspection (that it appears and polymer does the right things!)

Next steps: Get End-to-end working again! This involves:
- Fixing the socks-rtc / uproxy-networking references, now that they are no longer freedom modules. cc @iislucas
- Completing the polymer UI.