This commit refactors the majority of the Mapgen settings system.
- MapgenParams is now owned by MapSettingsManager, itself a part of ServerMap,
instead of the EmergeManager.
- New Script API functions added:
core.get_mapgen_setting
core.get_mapgen_setting_noiseparams,
core.set_mapgen_setting, and
core.set_mapgen_setting_noiseparams.
- minetest.get/set_mapgen_params are deprecated by the above new functions.
- It is now possible to view and modify any arbitrary mapgen setting from a mod,
rather than the base MapgenParams structure.
- MapgenSpecificParams has been removed.
