Assorted tsmf and gstreamer fixes

* tsmf audio volume fixes
  * The first audio volume message is received before everything is
    initialized.  Cache this data until we're ready.
  * Handle the cases of gstreamer unitialized/partially ready/
    fully ready.
  * Default to 50% as a fallback if the above fails.
* Improved detection of the primary monitor.
* Fix an unexpected shutdown when the server asks us to resize the media
  overlay to (width=0,height=0).
* Permit multiple presentations - required for repeat of audio files
  and also is seen in some video cases.
* Several leak fixes.
* Fix logging related compile warnings and other usage of PRIu64.