Q1BSP: use compatible collision detection

Q1BSP: make the player's bbox fit the player's cliphull

This is necessary for correct collision behaviour (otherwise the player's "head" can poke into ceilings).

Also sets the correct bbox on Q2BSP and disables crouching on Q1BSP.

Q1BSP: use cliphulls for collision detection

Implements #2895 (closed)
Fixes various collision problems on Q1 maps.