Add translation to Catalan

[OndoAlvelle]

Translated both the base strings and the extra folder. I left the app name in English but I also have a pun I could use in Catalan if you're ok with it ("Recordànec", it's just a literal translation, which happens to work well in Catalan too).

[matfantinel]

Thanks for this! Gonna make sure it's pushed in the next release.

About the name, it's great that it's translatable, but I think it could be confusing having the app be called different things - like for example someone searching for it on the web AppCenter, or even here on GitHub for example (where it would always be in english).