Update the Catalan translation and squeeze some of its strings.

This PR updates the Catalan translation and squeezes some of its strings
to better save screen space. There is a bug I can't solve, though. In
the 'welcome' screen, the left button has some of the text hidden, due
to the long strings I had to use in this translation. I tried finding
other equivalent words, but would make the translation quite confusing.
Maybe the button can be expanded a bit to accommodate the strings?

Cheers.