drivers/tone_alarm and tune_control small improvements/cleanup

- drivers/tone_alarm: move to ModuleBase and purge CDev (/dev/tone_alarm0)
 - drivers/tone_alarm: only run on tune_control publication (or scheduled note) rather than continuously
 - drivers/tone_alarm: use HRT to schedule tone stop (prevents potential disruption)
 - msg/tune_control: add tune_id numbering
 - systemcmds/tune_control: add "error" special case tune_id
 - move all tune_control publication to new uORB::PublicationQueued<>
 - start tone_alarm immediately after board defaults are loaded to fix potential startup issues
 - for SITL (or other boards with no TONE output) print common messages (startup, error, etc)

platforms/common/include/px4_platform_common/px4_work_queue/ScheduledWorkItem.hpp

@@ -44,6 +44,8 @@ class ScheduledWorkItem : public WorkItem
 {
 public:
 
+	bool Scheduled() { return !hrt_called(&_call); }
+
 	/**
 	 * Schedule next run with a delay in microseconds.
 	 *
@@ -59,6 +61,13 @@ public:
 	 */
 	void ScheduleOnInterval(uint32_t interval_us, uint32_t delay_us = 0);
 
+	/**
+	 * Schedule next run at a specific time.
+	 *
+	 * @param time_us		The time in microseconds.
+	 */
+	void ScheduleAt(hrt_abstime time_us);
+
 	/**
 	 * Clear any scheduled work.
 	 */