aurafilter: filter out debuffs when the caster is nil

For auras cast by players not in the player's group the caster value is nil.
For environmental effects the caster is the target.
debuffhighlight: reworked the element as isBossDebuff turned out to be something else

Renamed to DispelHighlight
Now only works for players with dispel capabilities
Turned icons off for now since they do not provide much information
ClassIcons: monks can have up to 6 chi now
Use Rebirth instead of Innervate as druids click cast spell

The latter got removed in wod