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/modules/land_detector/LandDetector.cpp

@@ -55,7 +55,7 @@ namespace land_detector
 
 LandDetector::LandDetector() :
 	ModuleParams(nullptr),
-	ScheduledWorkItem(px4::wq_configurations::hp_default)
+	ScheduledWorkItem(MODULE_NAME, px4::wq_configurations::hp_default)
 {
 	_land_detected.timestamp = hrt_absolute_time();
 	_land_detected.freefall = false;