Implement a working MPRIS DBus connection with a separate API to control it. Right now only player playback state is reflected and Play/Pause/PlayPause calls work.
Gst.Uri.get_protocol function is very simple. It just splits string by ":" and return the first part. We can do the same in JS and by doing that we do not have to initialize GStreamer just to get this function.
Otherwise GStreamer will error out and playback will stop. Non-existing subtitle file is common on Flatpak when user tries to open/drop a file from a folder that container does not have access to.
Play video with external subtiles by:
* selecting and opening both video+subs from file chooser/manager
* dropping subtitles file on player window
* opening subtiles from file chooser/manager while video plays
* send their file path/uri to player via WebSocket message
The "clapper_src" directory name was unusual. This was done to make it work as a widget for other apps. Now that this functionality got removed it can be named simply "src" as recommended by guidelines.
