Added catalan

Warning: Seems like ISO 3166-1 alpha-2 has not value for catalan. The "ca" code is for Canada (http://en.wikipedia.org/wiki/ISO_3166-1_alpha-2#CA)
So http://www.famfamfam.com/lab/icons/flags/ has no icon for catalan.

I didn't find documentation for compile and test the changes so I don't know if it works.
I have opened a question: http://stackoverflow.com/questions/24994017/contibuting-jhipster?noredirect=1#comment38858851_24994017

If you would tell me where I can find the corresponding docs I will try to check my changes and I would try to find a work-arround for ISO 3166 issue.

Best regards,
Ignasi