Rework xpmp "prefs"

[kuroneko]

xpmp at the moment uses a hook provided with the system it's integrated with to get various configuration and preference details.

This is almost certainly a lingering remnant of the fact it was once part of the XSB codebase.

Configuration state should be internal, and the integrator should call an API to change it the values, and this way, changes that require large internal state changes (such as changing texture resultion or filtering mode) can trigger edge triggered behaviour to correct the internal object state.