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

Add check for datatype overflows
use native datatype indices instead of fixed 16bit/32bit ones

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.