Specify a background color for the Persona dialog (bug #1202483)

https://groups.google.com/d/msg/mozilla.dev.identity/01aAVasAOpc/ZtiBlWEX9NYJ
http://identity.mozilla.com/post/55796551587/persona-a-login-that-matches-your-site
Disable identica photo importer (bug #1200599)

Identica has moved to a different platform and the importer doesn't
work anymore.
Updated Turkish translation
Add a new British English translation
Update the POT file with the latest strings