Feature Request: disable one of video or audio by setting.

[mscout1]

We only want to use this for AUDIO for now. For video, we are using a youtube embed widget.

We only setup the our StreamFields with AudioChooserBlock, and that's fine. It will protect us from some writer costing us video bandwidth.

We would also like to protect our storage by preventing video upload. At first I thought that setting VIDEO_EXTENSIONS to an empty list would prevent any files from being uploaded, since no extensions were whitelisted. Instead, it allowed all extensions.

Ideally, we would also like to hide the "add video" button to fully prevent confusion.

I would suggest that an empty list in *_EXTENSIONS setting should hide the button and disallow all uploads. None can still allow all if that is desired.

For now, out work around is to set VIDEO_EXTENSIONS to ["video_upload_disabled"]. That still allows a tricky bad guy to upload a file, but at least it prevents accidents.