Added Basic Branding Support

The logo is now easily re-branded. Updated README to include info for additional customization.
Merge pull request #199 from edx/theming

Added Basic Branding Support
Upgraded to Django 1.7

- Changed syncdb to migrate
- Upgraded Django Debug Toolbar and completely gated usage behind environment variable
- Using updated version of Django Announcements
- Updated blocktrans to use trimmed parameter