vtl: update export information
vtl: remove xjadeo option dialog

xjadeo options (selective session restore) are only
useful for testing and debugging.
vtl: remove video-maintenance menu

* only really relevant for testing/debugging.
* the back-end functions are still used for 'normal' operation
  and called implicitly when opening/closing a video.
* call stop_video_server() when removing a video.
vtl: update session start/end only when adding (or dragging) the video