[refactor] Split MobManager.cpp into MobAI.cpp and Combat.cpp

This is terrible. It was a mistake to do this before cleaning up the
actual code. It might be better not to use this commit and to do this
refactor in a different order or something.

src/NanoManager.cpp

@@ -3,7 +3,7 @@
 #include "NanoManager.hpp"
 #include "PlayerManager.hpp"
 #include "NPCManager.hpp"
-#include "MobManager.hpp"
+#include "Combat.hpp"
 #include "MissionManager.hpp"
 #include "GroupManager.hpp"
 #include "Abilities.hpp"