i18n: Merge Catalan translation from fedora.zanata.org

i18n: Merge Catalan translation from fedora.zanata.org

Merged with this command, which takes new translations from the Zanata
version, but doesn't take changed translations, except when they clear
the fuzzy flag from a translation:
    msgcat --use-first po/ca.po po/ca.po.zanata -o po/ca.po

I also manually copied new translator names to the header comment. I
didn't update the header key/value section, but here are the interesting
bits from the Zanata version:

"POT-Creation-Date: 2015-10-06 16:57+0200\n"
"PO-Revision-Date: 2019-07-25 10:42+0000\n"
"Last-Translator: Robert Antoni Buj Gelonch <rbuj@fedoraproject.org>\n"
"Plural-Forms: nplurals=2; plural=(n != 1)\n"