mode api: Remove most modes from the chmode_table, and have them initialized in modes...

mode api: Remove most modes from the chmode_table, and have them initialized in modeset files.
Modeset files are modules stored in shadowircd/modes. All they do is initalize
a set of modes on load, and orphan said modes on unload.

All cmodes not included in ircd-ratbox are now located in modeset files, rather
than being in the core. These modes no longer simply use defines, their
locations are stored in a the new struct module_modes. Each of these is set
when intializing the mode in the modeset files, and set to 0 when orphaning
the mode upon unloading the modeset file.

In addition, use_forward has been removed, as it is now obsoleted by modesets.