[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/task_client_state.cpp

@@ -2727,3 +2727,17 @@ bool ClientTaskState::HasActiveTasks()
 
 	return false;
 }
+
+void ClientTaskState::LockSharedTask(Client* client, bool lock)
+{
+	if (m_active_shared_task.task_id != TASKSLOTEMPTY)
+	{
+		ServerPacket pack(ServerOP_SharedTaskLock, sizeof(ServerSharedTaskLock_Struct));
+		auto buf = reinterpret_cast<ServerSharedTaskLock_Struct*>(pack.pBuffer);
+		buf->source_character_id = client->CharacterID();
+		buf->task_id = m_active_shared_task.task_id;
+		buf->lock = lock;
+
+		worldserver.SendPacket(&pack);
+	}
+}