"Delete file" button and context menu item added. Deletes downloaded file.
When you play the file it marks as "L" (Listened)
Now new podcast series are bold and listened are oblique.
Bugfixes
Actions with PodcastItem properties moved to PodcastLogic.
Refactoring, bug fixes.
Now all data for GUI are taken from memory instead of reading from db every time.
Fixed bug when DatabaseDL created object IEnumerable<Podcast> which contained Items as DataRowCollection instead of List<>.