Massive UI Improvements

A lot has changed in the past week as I've been without my main laptop.
Still, I've been pushing changes in order to improve the interface of
the app. It now embraces flat design and gets rid of shadows and is
cleaner.

-Body is full bleed: there are no shadows. The content and toolbar take
up the entire width of the screen
-Header is lighter
-Panel and main section now use DIVs instead of table cells
-Metadata elements are more responsive
-Design more responsive to browser resizing
-Fixes to Idea panel
-Improvements to themes
-Default theme now has flat buttons
-New Spotify panel available in the Store
-Other UI and bug fixes