Cancel an audio upload that is still processing

Stops the transcription of the scout's own audio while it is processing: the audio becomes CANCELLED, results that arrive later are ignored and create no deals, and the scout gets the transcription-cancelled Pusher event. The results already saved (its rows, clips, the audits they leave empty, its chunk records and its transcript file) are removed in the background, and the scout gets the transcription-results-removed Pusher event when that is done. The removal stops, removing nothing more and sending no event, once a scouting report holding the audio's rows is approved. Cancelling an audio that is already cancelled succeeds again and queues that removal again when some of its results are still there, e.g. when queuing it failed the first time. Refused for an audio of another scout and an audio with no scouting report; approving a report removes its uploads from it, so this includes an audio whose report was approved. An audio not yet cancelled is also refused when it is on any approved report or is not processing.