Investigate offline content caching

[addyosmani]

Over on http://berry-app.appspot.com/, Service Worker caching using mobile toolkit currently only works for static local assets like the shell. I'm trying to also cache all responses from the Dribbble API too (my main content) but am unsure where one would configure this in toolkit's world. I've pinged the Angular Mobile team for pointers. Offline is only really useful with content.

In sw-toolbox, we ask people to just set origins they want cached in Cache API using express style routes and this avoids needing to do too much additional work that could end up in the Cache API yourself (takes about 2m to setup). I think issue-zero may have manually cached content in Local Storage but could be wrong.