Minor code fixing, reworked unit targeting method and a new enum class
New class ResourceType to replace the old way to define a resource (String).
When adding a new target to the effect, the effect will check if it can be applied on friendly and/or multiple units.
Moved resolveTarget method and its depending methods from Game.java to MessageHandler.java and renamed the method to handleTargets.
Merge remote-tracking branch 'origin/GameCodeimprovements' into GameCodeimprovements