Formspec input for each individual noise parameter and flag.
Allow noise flags to be set in advanced settings, previously only settable
in minetest.conf.
Standardise 'group format' for noise parameters set in minetest.conf, as
only these support noise flags. However the older 'single line' format is
still accepted to support existing minetest.conf files.
Therefore auto-generate minetest.conf.example with noise parameters in
'group format'.
Setting 'type' in settingtypes.txt is now either 'noise_params_2D' or
'noise_params_3D', the dimension number is displayed in the advanced
settings edit page.
This unifies the settings APIs.
This also unifies the sync and async registration APIs, since the async
registration API did not support adding non-functions to the API table.
