Fix bookmarking

1. Bookmarking/favoriting works client side, but at this moment, not server side.  When a user tries to favorite an image, the client shows a error toast notifying the user that the image can't be favorited and visually undoes the action.  So the user can see they *can* favorite things, but something is going wrong during save.

2. Cleaned up searching and Flux-ified the ApplicationStore by removing all non-lazy fetch methods.

3. Made the highlighting of sidebar navigation more explicit for now, but added a todo item (in the code) to move all the route-to-nav-highlighting code to a RouteConstants object for for DRY behavior in the future.