Update _job_changed to changed _event_mapping
Move extend() to udiskie.common
Remove the happen'ing' events

These were not used internally. Furthermore, status updates for the
actions monitored by udiskie (mount/unlock/...) are not very useful.
Possibly, a job_started event will be added sometime.
Remove the object_added/object_removed events

These were only provided in the udisks2 wrapper for internal use. The
object_removed was not even implemented as far as I can see.
Remove obsolete mainloop declarations
Remove Job struct for udisks1
Fix _device_job_changed

Delete the job also when it failed.
Cache jobs to avoid duplicate events
Enable unmount/lock notifications in udisks2 for external jobs
Check job completion before triggering event in udisks2

Sometimes the device properties are changed after the Job.Completed
event is triggered by UDisks2 (bug?).
Merge branch 'bugfix'