Refactor player groups

Group structures are used now. Adds more checks in some places but simplifies things overall.
We can expand this system to entities as well now pretty trivially.

src/Combat.hpp

@@ -25,5 +25,5 @@ namespace Combat {
     void init();
 
     void npcAttackPc(Mob *mob, time_t currTime);
-    void genQItemRolls(Player* leader, std::map<int, int>& rolls);
+    void genQItemRolls(std::vector<Player*> players, std::map<int, int>& rolls);
 }