Added CombatManagerService and pulled out core functionality from UI

[herrozerro]

Added a CombatManagerService that exposes the core functionality.

• List of combatants. Tracking current and next
• Save, Delete, Sort Combatants
• Advance Turn
• Track Rounds

Stripped out any references to the above in the GUI and let the service manage the combat. The GUI still has a lot of UI specific code which is fine. But using this service it can be extended to other UIs

I don't know if this satisfies #5 or not, but if not maybe it should be changed to drop the WPF, as this commit puts core functionality into a service and can be used in other patterns including MVVM for WPF.