add /loadalign load with player orientation; add reporting of missing mods to /load and /allocate

as described in my recent posts on the forum (https://forum.minetest.net/viewtopic.php?p=142405#p142405  and https://forum.minetest.net/viewtopic.php?p=142426#p142426) with some changes to the original code, and much more bug testing.
The main problem is the new /loadalign code hasn't been tested with old-format schem files (ie prior to version 4), but should work. If it doesn't an option for slightly more robust (but slower) code is included. Worst case, the original /load can be used, as basic function has not been changed (just added pass-through and notification of missingMods).