Add alphabeticaly sorted worldlists
Select world after creation
Move worldlist handling to separate file
Merge world selection of singleplayer/server tab
Remove some useless code

This reverts commit 39d03148.

Always use address for server
Fix first (empty) element beeing selected after deleting last world

make enter button work in create world dialog

On the lua side, notably minetest.env:<function>(<args>) should now
be replaced by minetest.<function>(<args>).
The old way is and will stay supported for a long time.

Also:
Update and clean up lua_api.txt (by celeron55)
Move EnvRef to lua and remove add_rat and add_firefly (by kahrl)
Add separate src/util/CMakeLists.txt, other minor fixes (by kahrl)

Add a Way of checking for specific Feature with Lua Adds minetest.get_feature() and minetest.has_feature()

When accidentally misspelling a name, privileges are sometimes granted to non-existent players, leaving them with the extra privileges, but without the default privileges, if they ever join the server. This corrects that by disallowing /grant from working with invalid players. For completeness, it does the same for /revoke.

When first entering an area, sometimes placing nodes replaces other nodes that are not buildable_to. This seems to be caused by the fact that nodes in unloaded map blocks are treated as ignore, a node that is buildable_to. This fixes that, by using get_node_or_nil() instead of the previously-used get_node(), then checking to see if the nodes were actually loaded before replacing.