rap-worker: Ensure status directories are created

In some cases, it was attempting to create a status file in a directory
that did not exist yet.
recording: Add a 'mkclean' step to video generation

The 'mkclean' tool reorganizes the encoded webm file to optimize it for
streaming. In particular, it moves the index to the start of the file.

This fixes streaming in Chrome, which otherwise had a very long delay
before playback started since it downloaded until it saw the index
before it started playback.

This needs a new dependency added to the bbb-record-core package to
pull in the mkclean tool.