Add group system

Initial commit, not tested in multiplayer yet. Some revisions still left
to do.

SQF/dayz_code/groups/rejectGroup.sqf

@@ -0,0 +1,16 @@
+private "_uid";
+_uid = getPlayerUID player;
+
+//Remove all invites to this player
+{
+	if (_uid == _x select 1) then {
+		dayz_activeInvites set [_forEachIndex,"delete"];
+	};
+} forEach dayz_activeInvites;
+dayz_activeInvites = dayz_activeInvites - ["delete"];
+
+_this ctrlShow false;
+
+//Sync change to all remote machines (less data than sending whole array)
+PVDZ_groupInvite = [false,_uid];
+publicVariableServer "PVDZ_groupInvite";