Implements naval factory and unit support.

[CCHyper]

Closes #531

This pull request implements various features for naval factory and unit support.

NOTE: Until a VesselClass is fully implemented, The following keys will act as a separation between vessel factories and water-based UnitTypes (VesselTypes), with the aim of providing basic naval feature support.

At this time;

• Rules: [General] -> BuildNavalYard=<BuildingType list>

  • A list of BuildingTypes that are considered a NavalYard for AI production purposes.

• Rules: [General] -> AINavalYardAdjacency=<integer: cell distance>

  • The distance in cells the computer player can place a Naval Yard (as set by BuildNavalYard) from their Construction Yard.

• [BuildingType] -> NavalYard=yes

  • An initial random rally point will be set at a distance of 2 cells away when the structure is placed.
  • Will allow the player to set rally points on water rather than land.
  • Allow the building to be assigned as "Primary" alongside a normal UnitType factory.

• [UnitType] -> Naval=yes currently has no effect, but it is recommended that you define this on all water-based UnitTypes to ensure an easy transition when this feature is extended.