This also cleans up settings a bit

Remove flagmask field from set_mapgen_params table
Add small bits of needed documentation

Add checks for invalid user input for important settings
Rename Settings::tryGet* to Settings::get*NoEx for consistency

This reverts commit 3f376a09.

Rename try* non exceptioning functions to *NoEx

MapgenParams is no longer a polymorphic class, eliminating the need for messy and bug-prone reallocations.
Separation between the common and mapgen-specific parameters is now strongly defined.
Mapgen parameters objects are now properly encapsulated within the proper subsystems.

  -add client states to avoid server sending data to uninitialized clients
  -don't show uninitialized clients to other players
  -propper client disconnect handling
Minor comment fixes in server
Minor bugfixes in connection
  -improved peer id calculation
  -honor NDEBUG flag
  -improved disconnect handling
  -increased initial send window
Remove some dead code

The real problem was that MapBlocks were not activated before getting sent to the client

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)

Concatenate the thread id as string instead of adding it to the pointer