Added Fahrplan to Transifex

I have [added Fahrplan to Transifex](https://www.transifex.com/projects/p/fahrplan/): this is online localization platform where people can request to join a team and contribute a language. A-la GitHub, but for translations.

I have also imported an updated German and Romanian translations from there, plus added a separate credits line for translators into `about.js`.

Also, let me know if you'd like me to add you as a maintainer of Fahrplan on Transifex (you'll have to register there).

PS: Ukrainian and Russian translations were updated, too.