Support Audiobookshelf

[radonmiser]

Is your feature request related to a problem? Please describe.
1.Player progress is not detected
2.Subtitle files under Library files is not loaded for user to choose from

Describe the solution you'd like
1.Detect the Audiobookshelf player
2.Load all subtitles under Library files if available(they can be identified through file extension and there's a download button)

Additional context
https://github.com/advplyr/audiobookshelf/
There are some efforts on audiobookshelf to support subtitle viewing.
I am not knowledgeable enough in this to know if they have any impact on my feature request.
advplyr/audiobookshelf#2919