Multiplayer fixes

Improved stickiness of mob targetting, making stun-locking golems much harder

Healers now heal 1 more HP per 20 levels of Gnome Damage

If their owner is on full health, Healers will now heal teammates - this should stop DPS-focussed characters ressing gnomes they don't need, just to stay alive.

Gnomes are now much faster on Fluffy difficulty. Medium retains the previous movement speed, and the top 2 difficulties are slower; this means that points spent in Gnome Movement Speed aren't wasted.

Mage Gnomes now return mana in an identical way to Healers, including sharing Mana regen amongst the team.

Bunch of optimisations to Critter wandering

Sleeping Mobs will now wake up when you're within 50% of their attack range, instead of a fixed 4 metres. Melee mobs still wake up at 4m.

Fixed Story text and Level text for Shared/Split/Single cameras