ChapterDb plugin updates

This implements the GetChapters method, but there is still an issue. The core ChapterManager.Search method on line 127 -  the foreach attempts to set Id and ProviderName, but the results in FFProbeVideoInfo.DownloadChapters doesn't reflect the updated info (line 499). From there the id split fails and it doesn't work. Once that is fixed this should be good to go.

I also made some tweaks to get the best matching results based on the playback time. I haven't done anything with the MD5 hash yet - I wanted to see how this worked first.