[Shared Tasks] Implement Activity Locking (#2339)

* Add shared task element locking

This adds the `lock_activity_id` field to the tasks table which will
automatically lock a shared task when that element becomes active.

A method was added to world analogous to zone's UnlockActivities to
determine when an activity is active with respect to task steps.

Also adds quest apis to manually lock or unlock a client's shared task

* Add comment

zone/lua_client.h

@@ -333,6 +333,7 @@ public:
 	bool IsTaskCompleted(int task);
 	bool IsTaskActive(int task);
 	bool IsTaskActivityActive(int task, int activity);
+	void LockSharedTask(bool lock);
 	int GetCorpseCount();
 	int GetCorpseID(int corpse);
 	int GetCorpseItemAt(int corpse, int slot);