Add Mirror Image/Clone ability for wizard boss

[eqbech]

Add spell for boss to create $n$ clones. Ideas for specs of this ability:

• Clones should have the same set of abilities as original, meaning they can cast all spells the original can except from cloning further themselves.
• Clones should have % of boss health i.e they are weaker and encourage killing these first.
• They have a set timer after which they despawn, this would mean the player ignores killing them but would have to handle/dodge the abilities they cast.