This is a pretty big change all around. The gist of it is that it moves the mobility_flags into traits or variables that can track the sources, and to which we can append code to react to the events, be it via signals or via on_event-like procs.
For example, MOBILITY_STAND could mean, depending on context, that the mob is either already standing or that it may be able to stand, and thus is lying down.
There was a lot of snowflakery and redefinitions on top of redefinitions, so this is bound to create bugs I'm willing to fix as I learn them.
The end-goal is for every living mob to use the same mobility system, for the traits to mean the same among them, and for no place to just mass-change settings without a way to trace it, such as with mobility_flags = NONE and mobility_flags = ALL
Fixes AIs being able to strip nearby people. They've lost their hands usage.
