Add Polish as a supported language
Add Polish as a supported language

We already had some Polish translations, that were currently not
available to users. Adding it here because it helps me debug some
issues regarding language with more than one form.

dreampet/gitlab,jirutka/gitlabhq,mmkassem/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,axilleas/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,dreampet/gitlab,dreampet/gitlab,mmkassem/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,stoplightio/gitlabhq,jirutka/gitlabhq,mmkassem/gitlabhq,iiet/iiet-git,stoplightio/gitlabhq,axilleas/gitlabhq,axilleas/gitlabhq,dreampet/gitlab,iiet/iiet-git,axilleas/gitlabhq,iiet/iiet-git