Add a new site

Add new site created with Mezzanine
converted ratios to floats

ratios were integer division, which didn't work as desired. casting the numerators to floats cures this ailment
added padding color option into thumbnail tag
More thumbnail tweaks - don't prefix image's thumbnail subdirectory and comment the reasoning for the sub-directory, use hex strings for color and include in thumb name, and pep8 fixes.
Document optional thumbnail tag args
Minor fixes for building docs.
Added pythonbc.co to sites in README
Fix thumbnail test
pep8 fix
Added USE_L10N check for language dropdowns in admin.
Added mezzanine-agenda to third party apps list in README.
Merge
Fix USE_L10N check for admin language selector.
Handle null descriptions ofr settings in conf form.
Added www.theartrebellion.com to sites in README.
Catches exceptions in thumbnail image.convert
Prevent some warnings during tests
Restructure content architecture docs - lead in with describing how Page/Displayable are built and used.
Move short_url generation code from template tag to model, so we can use it for tweets.
Added TweetableAdminMixin and applied to BlogPostAdmin - used for sending tweets from admin.