Changed base_soldierarena to base_arena, made more general.

This is now a general arena rather than the Soldier / Demoman exclusive soldierarena it once was.

New globals:
SCORE_PER_KILL changes the score per kill. Default is 1.
DISABLE_SELF_DAMAGE prevents RPGs, GLs and PLs from damaging self. Default is true.
DISABLE_FALL_DAMAGE prevents fall damage from occurring. Default is true.
CLASS_LIMITS is a table of classes to use for limits. Default is all classes active, no limits.
AMMO_DETPACK is the amount of detpacks to give. Default is 1 / true.
AMMO_JUMPPAD is the amount of jumppads to give. Default is 0 / false.
AMMO_GREN1 is the amount of frag grenades to give. Default is 1.
AMMO_GREN2 is the amount of secondary grenades to give. Default is 0.
Merge 3 branches, fix sync issues.