Fix #2196 Missing `python-brace-format` for xml-extracted strings

Introduces new dependency `polib` for python in the create_pot
toolchain. Sorry about that, but I did not find a better way.
Tools like `msgfilter` do not allow changing the entry flags at will, or
at least I did not find a way of doing so.

Apparently polib also does funky stuff about line wrapping when saving
the file again, but I'll take that as one-time chuff.

At least we can also remove two lines in sql-extract script in return...
Translations: New templates

Generated by ./development/create_pot.sh