Transifex support

Builds on Mike's previous pull request.

Its an awesome translation platform which we use for the rest of core.
Comes with a nice UI for translators, and fetching new translations
is as easy as executing "tx pull -t && git add && git commit" on the commandline.
The assumption is that the module maintainer actually does that of course :)
Marcus/Andrew, I'm happy to add you as language maintainers if you sign up
to transifex.com.