Added slow monsters, the inverse of fast monsters

This is a skill setting only, no "always slow" or "never slow" actor
flags, and no DM flags.
Added slow monsters to Strife's easiest skill
Added slow states to relevant Strife monsters

Namely, acolyte, shadow acolyte, reaver, stalker, and turret. Info on
which states needed the slow flag was obtained with Quasar's permission
by looking at G_InitNew() in g_game.c and the info.c state tables from
Chocolate Strife.
Also added fast flag to acolyte states that needed it, based on the same
source.
Merge branch 'slowstate' of https://github.com/Gaerzi/zdoom