Adding stable/l10n-kf5 translations for "krita/3.0" branch

[Friedrich W. H. Kossebau]

Hi translation admins,

seems we forgot to set up translations for stable/l10n-kf5 when Krita 3.0 was 
branched off.

The branch name for the stable release version is "krita/3.0".

Please add that in the setup.

If I learned things correctly last WE that the fix would be to add in 
branches/stable/l10n-kf5/scripts/get_paths for the function get_branch an 
entry like this?
	calligra_krita)
		echo "krita/3.0"
		;;

Though seems also other functions need more fixes, when I compare to the 
get_paths one for trunk, e.g. get_po_path and get_path

Well, you know your scripts and I for now better try to not also mess around 
there :)

Cheers
Friedrich