Enable markdown for photo descriptions
Merge remote-tracking branch 'upstream/master'
Merge branch 'locales'
Should probably be in alphabetical order
Send HTTP caching headers for photo show
Bugfixes
Adds an action for sharing photos elsewhere with a public cache

This is targetted towards high traffic from places like Reddit.
By using a short URL, e.g. /p/104, or appending /share to the photo's
standard URL, we can use a different action which can be cached for everyone.

An improvement to this will be to asyncronously load the user's correct
nav if they're signed in. At the moment it's cached as a signed-out user.
Add better sharing options to views
Merge pull request #116 from robotmay/share-caching

Add better sharing support and other fixes.