Move episode file deletion to EpisodePersistence
Fix typo in method name
Do not copy the logo to another location
Typo in DetlefDownloadManager
Ensure podcast logos are not picked up by gallery
Remove silly try/catch block
Do not update the DB twice on download completion
Remove UNWANTED_CHARS clutter
Begin refactoring download manager

Split handling for different files into callbacks.
Finalize download manager refactoring
Update the episode storage state on deletion

The file and DB handling is somewhat confused.
Sometimes, DB functions delete files, which they shouldn't; sometimes,
file persistence functions update the DB, sometimes they don't. This
needs some further refactoring.