Add checks to see if a show directory has been updated

[makstermaki]

When the application starts, it first scans all of the passed in TV show directories and processes the media files. On a subsequent run, the application will see that it has already processed a TV show directory and would just skip it. Extra checks should be added so if the media files have changed, such as some files being deleted or new ones appearing, the directory is reprocessed and the channels are updated as needed.