Fix bug with last seen
Move header into Ember application

Birthdays page is still outside, need to pull it in later
Add offline readonly mode and offline checks.

Additionally added styling improvements.
Rename preload.js to image_assets.js
Preload and cache all models on app startup
Use Rails-Assets to manage JS dependencies

https://rails-assets.org/
Rollback Bower
Take out preloading for now (as it is still experimental)