Localization fixes

This pull request fixes two localization bugs. It adds a missing textdomain parameter and fixes some faulty logic concerning the localization of media gallery titles.
Hey @WTurunen Was being quick in reviewing.
Then I understood the reason behind the change.
GNU gettext parser is not PHP Parser & it cannot fetch the variable values.

Just one change: Can you please sync up the switch cases & their respective return values. They are not matching up.
E.g., `__('All Photos')` for `photo`, `__('All Music')` for `music` & `__('All Videos')` for `video`

Just for the reference:
http://markjaquith.wordpress.com/2011/10/06/translating-wordpress-plugins-and-themes-dont-get-clever/
http://wordpress.stackexchange.com/questions/81672/variables-in-translatable-text