Finished last of the 10 critical effects.

- Renamed GainBonusEffect to GainModifierEffect.
- Added support for multiple scores and GainModifiers on Target.
- Added defenses (Fort, Ref, Will and AC) to Your as well as AllDefenses.

Future:
- Need to add some more testing since only integration testing has been
  done on classes in the Effects namespaces.
- Need to add critical effects to the origins and update the renderer to
  use them.