Improvements in cover art search (TIO::parseCoverArt)
- add method to parse cover arts into sound file (extracting embedded covers)
This change is useful to handle existing users
emitting signal with trackpointer instead coverlocation
When user select a row in tableview it emit a signal to coverart class.

With this change we'll be able to know more about the current selected row.
It was impossible to use properly the search algoritms and covercache in cases when the signal was just an empty string.

This change is also to help handling existing users.
initialize coverArtDAO into trackcollection
CoveArtDAO improvements: handling existing users + cosmetic fixes
- add slot to look for covers always when the covercache doesn't find it.
- fix bugs in TrackDAO - we must always try to save the cover into db (cover_art table) before give the coverId to library updates.
- remove cover search from initial library scan (now we do it on demand)