Added effect concept.

This represents spells and other special abilities that modify a unit
for a given period of time.
Added constructors for Effects.
Added animation support for effects.
Test some new features.

Basically guaranteed a draw.
Verified the new effect system works on Troll regeneration.
Be able to animate effects.
Added healing effect.  Used by Troll regeneration.
Troll regeneration uses the generic Effect system.
Removed obsolete Regenerate action.

Any new action types like this can use the generic Effect action.
Testing a big battle with new units.