px4_work_queue: command line status output and shutdown empty queues

* adds a work_queue systemcmd that will bring a tree view of all active work queues and work items
 * WorkQueues now track attached WorkItems and will shutdown when the last WorkItem is detached

src/drivers/distance_sensor/ll40ls/LidarLitePWM.cpp

@@ -46,7 +46,7 @@
 
 LidarLitePWM::LidarLitePWM(const uint8_t rotation) :
 	LidarLite(rotation),
-	ScheduledWorkItem(px4::wq_configurations::hp_default)
+	ScheduledWorkItem(MODULE_NAME, px4::wq_configurations::hp_default)
 {
 }