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/tfmini/TFMINI.cpp

@@ -34,7 +34,7 @@
 #include "TFMINI.hpp"
 
 TFMINI::TFMINI(const char *port, uint8_t rotation) :
-	ScheduledWorkItem(px4::wq_configurations::hp_default),
+	ScheduledWorkItem(MODULE_NAME, px4::wq_configurations::hp_default),
 	_px4_rangefinder(0 /* TODO: device id */, ORB_PRIO_DEFAULT, rotation)
 {
 	// store port name