added code for custom download format (minus DB Host&PW&User)

[Ithanil]

DB_HOST, DB_PASSWD, DB_USER need to be set in bin/register-download-format!

Also, we use the following nginx locations: location ~* ^/video\/.+\/video-0.m4v { root /var/bigbluebutton/published; expires -1; add_header Content-Disposition "attachment; filename=video.m4v"; }

location ~* ^/video\/.+\/video-0.mp4 { root /var/bigbluebutton/published; expires -1; add_header Content-Disposition "attachment; filename=video.mp4"; }

[Ithanil]

Sorry, didn't want to create an upstream PR