Update copyright years in all mapgens
Add myself to copyright notices in mgv5 and mgv7

Decorations: Remove lower limit of water level for placement

Mgv5/v7: Fix generateBiomes biome recalculation logic Biomegen down to y = -192 for mgv5 deep oceans. Improve code

Mgv5: Add large_cave_depth constant

Add large pseudorandom caves below -256
De-link terrain level from water_level
Cavegen: Mgv5 large cave code

Caves check for biome nodes, only excavate stone under water level
Unease caves noises, use MT0.3 parameters
Blobgen after cavegen
Biomegen: remove 'is replaceable content' bool

This fixes biome surface in tunnels

Use/add stone_surface_max_y to speed-optimise/guide dungeon generation
MgV7: Don't let mountain terrain chop dungeons at mapchunk borders
Make mountain terrain update stone_surface_max_y for caves in mountains

Add support for notify-on-decoration
Clean up mapgen constructors
Clean up mapgen.cpp code style somewhat
Remove trailing whitespace from some files

Add BiomeManager, OreManager, DecorationManager, and SchematicManager

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.

mgv7: Implement getGroundLevelAtPoint(), fix layer of topnodes at chunk Y boundaries, remove growGrass()