Also rewrite mapgen registration for static initialization

Add minetest.get_mapgen_params()
Deprecate minetest.register_on_mapgen_init()

Fixes #1807: When the server list finishes downloading, the local server
list resets in certain conditions

Also set default height_min/height_max to -31000 and 31000,
respectively, for ore and biomes

Biome API: Add shore top and shore filler nodes, underwater node, water top node. Add water top depth and shore height parameters. Remove water dust node

Conf.example: Correct grammar and spelling. Shorten some lines. Move a few lines into correct sections. Remove finite liquid reference. Make indentation consistent

Increase indentation throughout file for clarity. Correct mistakes. Shorten lines. Make more consistent

Signed-off-by: Craig Robbins <kde.psych@gmail.com>