Convert general settings page to ember data

Issue #2846
-Implement custom RESTAdapter and serializer for settings data.
-Convert theme selector to Ember.Select.
-Finish upload modal and wire into settings page.
Could this text be a little more specific, as in "Upload successful" or something along those lines? Just put a blog logo up and kind of scratched my head when it said "Saved".  "What saved? Huh?" - I thought to myself.