Update to drugs and health effects

Added a (very) slow health regeneration, it refils around one third of
the health bar over a period of 1 real-time hour. This is to simulate
real-life wound healing over a more compressed time period for gameplay
purposes.

Moved the drug time checks over to the drug script with a hook into the
player update timer.

Reorganised some drug checks in the player update timer to work around
the new drug effect changes.