If liquid_queue_purge_time == 0 then disable the queue size limiting and make this the default setting
Additionally, liquid_loop_max now defaults to 100000

This also cleans up settings a bit

Improve error handling in saveBlock()

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.

The commit didn't work because the blocks weren't loaded yet.

This reverts commit 22dbbf0a.

Conflicts:
	minetest.conf.example

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

* Prevent graphical glitches on old servers
* Fix flowing of liquids with viscosity != 1 and range != 8
* Fix range = 0, no flowing nodes will appear