Implemented new critical syntax.

- Removed Conditionals from AttackPower (unnecessary for Gamma World).
- Changed CriticalHitBenefit on Origin from string to an EffectExpression.
- Changed CustomDocumentCharacterRenderer to render out the new synatx,
  including italicizing the power names.
- Renamed TestFluentPowers.cs to TestFluentCriticals.cs.
- Changed tests to load the criticals from the origins rather than hard
  coded tests.