Support for NPC's to use focus effects.

Implemented support for allowing most focus effects to now be usable
by NPCs (ie Heal/Damage focus, cast time, spell range ect) from
both spell buffs and items.
Rule for enabling spell focus is TRUE by default (Plenty of live NPC spell examples)
Rule for enabling item focus is FALSE by default.

Consolidated a number of redundant client / mob / Merc functions
to use the same pathway for calculating effect values.