Move i18n from LP to Transifex  

After having maintaining a Mixxx translation mirror on Transifex (TF) for half a year, i`m convinced
TF is a valuable addition to the dev-process, that can drive user contributions and provide a better product in the end.

**What is this PR about**
* Make the latest translation available, provided by Transifex. The latest (as of 02-01-2014) matching translations from LP where merged using the TF translation memory).
* Create the preconditions for a further automation of the translation processes

**So, whats so nice about TF?**
* Free for OSS
* Easy to use for translators and maintainers
* Being actively developed and supported
* High success rate with other OSS projects
* Contributors can use existing social login credentials (FB, G+, Twitter, …)
* Translation memory ( 100% matching terms were filed from our existing translations)
* Multi-lingual glossary ( EN_US already filled with the terms from our manual)
* Machine Translation via BING (already active)
* Fuzzy translation with suggestions
* Translators are forced to sign our app-store CLA before contributing
* Periodically pull new translation sources from Github
* Notifying contributors about updated sources
* Transifex CLI & API available

**What still needs to be done?**
* (Optionally) Create mixxx-i18n repo. I`d prefer that, because we could use that repo
  for all kind of sub-projects like website & manual translation.
* Configure a cron to periodically, update the translation template at GH,
  pull translations from TF, and commit changes to GH. See  http://help.transifex.com/features/client/devel.html#user-client-devel
* There is also a [jenkins-plugin] (https://github.com/jenkinsci/transifex-plugin), as well as a
 [Sinatra server](https://github.com/jsilland/txgh) available that serves as a bridge between TF and GH
 (have not looked into that yet).

**Who are the TF maintainers**
 * Currently @esbrandt & @rryan