Add Catalonian .po file

[piponazo]

Final task related to #527

[clanmills]

Great. That has to be the simplest change in the history of the project. Of course, the work performed by Toni isn't simple or small. However the integration is a snap!

[codecov]

Codecov Report

Merging #544 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #544   +/-   ##
=======================================
  Coverage   63.48%   63.48%           
=======================================
  Files         154      154           
  Lines       20643    20643           
=======================================
  Hits        13105    13105           
  Misses       7538     7538

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