Have the recording archive delete originals of archived media

After the last segment of a recording has been archived, it is safe to
delete the original files that were recorded by the various media
handling components. This patch deletes the freeswitch audio files and
kurento webcam/screenshare files after they have been archived.

It needs to be used in combination with some changes to users/groups and
directory permissions to allow the `bigbluebutton` user to delete files
that it could previously only read.