Optimized minetest.get_connected_players()

Instead of collecting all objects within a huge radius (which could be
a big value), just register each player that connects and give back the
current hold list.
Remove mapgen_air alias (#935)
FIx wrong error message on invalid use of the formspec element image_button
Add Czech language
Translated using Weblate (German)
Translated using Weblate (French)
Translated using Weblate (Dutch)
Translated using Weblate (Chinese (China))
Translated using Weblate (Portuguese (Brazil))
Translated using Weblate (Dutch)
Translated using Weblate (Portuguese (Brazil))
Translated using Weblate (Spanish)
Add support for parameter 'visual_scale' for drawtypes 'signlike' and 'torchlike' like used for drawtype 'plantlike'
Fix minetest.facedir_to_dir when param2 is 5 or 7.
Add tool callback
Fix object duplication bug (at least in the most reproducible UFO case)
Remove vector metatable setting

This not only makes the vector functions faster, but also makes them more
consistent with other functions.
Add sanity checks to vector functions
Masterserver update
Masterserver totals fix