Monster database, spawn areas and roaming strategy

I just implemented:

• Spawn areas defined in map files
• Reading monster properties from a JSON database file
• The roaming strategies RoamMap and RoamArea
• The spawn strategies ReplaceSingle and ReplaceAll

I still need to implement the reading of game system specific monster properties. Next stop is attacking.

Oh, and the JSON parser need to be made more stable. When they miss some value, they spit out a stack trace. They should use a reasonable default and output a warning instead.