Establish a webservice allowing auto-update for Gui localizations by relaying between Transifex and Github

[assem-ch]

As we are using now Qt localization way with ts files, we need to use transifex for localization instead of launchpad. Transifex is not importing messages catalogues automatically from the source code. Though, we can implement a web service doing it by using the library txgh;

the library updates message catalogues in Transifex at each commit in Github; and commits the updated localization files in github at each change in Transifex.

There is an article explaining how to establish the webservice and configure the web hooks in both github and Transifex: http://blog.transifex.com/post/67760039192/github-transifex-integration

The library source code is here: https://github.com/jsilland/txgh

[assem-ch]

Transifex offers now a way to do this so no need to reimplement it, just follow the integration doc https://docs.transifex.com/integrations/github