Cleaner UI

I made a lot of changes to the user interface, including:

General design:
- Better typography and some placeholders for future information
- A new color scheme, rounded corners in the right places, a centered interface
- A lighter green flag pane on startup
- The "loading" hint is far more discreet

UI:
- Icons on the buttons, which are now in the top-right corner
   - TODO: Fork DjangoBB button css for site-wide uniformity
- Unicode glyphs for the iPad arrow locations
- A "smart" input field for the project ID which turns red if the project ID isn't a number
   - TODO: Make it send an xhr to validate the ID server-side; and also accept complete URLs instead of just the ID