Add debug logging to help diagnose playback issues

[bikegriffith]

Simply register a global window.ClapprRTMPLog function, which will be called from the swf via ExternalInterface to see log messages, e.g.:

<script>
function ClapprRTMPLog(msg) {
  console.log("[clappr-rtmp-plugin] " + msg);
}
</script>

[flavioribeiro]

@bikegriffith what happens if ClapprRTMPLog function doesn't exist on the window context?

[bikegriffith]

Seems to just fail silently in my testing

[flavioribeiro]

also, I'm wondering if https://github.com/video-dev/clappr-rtmp-plugin/pull/98/files#diff-7dfb85a40bf4906bf76c43e666dea9e6R398 shouldn't be placed inside the CONFIG::LOGGING block. In practice, it should always be a way to have a no-debugging build for production purposes.