Added Range for fluent AttackTypeAndRange creation.

- Removed AddAttackTypeAndRange that took an AttackType and string range.
- Changed powers to use the new Range object.
- Added TestRange to test Range.cs.
Changed AddPower to NovicePower in Power.

- Removed AddPower() and added NovicePower in its place. The intention is
  to specify powers using properties for NovicePower, UtilityPower and
  ExpertPower. Power remains an IPowerSource supplying the novice power
  (only) since there is no Level01 class to be a power source.
- Added NullPower for easy testing.
- Removed the required origin and required level checks from Power. They
  were more appropriate for D&D, where powers could come from multiple
  sources. In Gamma World, they only come from origins (apart from basic
  attack and second wind).