WCoverArt - fixing bug introduced by last changes - qMakePair cannot receive empty qstring as ""
DlgCoverArtFullSize - remove margins and spacings
DlgTrackInfo - implements closeEvent - closing DlgCoverFullSize when DlgTrackinfo is being closed
DlgTrackInfo - allow revert cover art change (when changes are canceled)
- WCoverArtMenu emits signal when coverLoc changes
- DlgTrackInfo update the current coverLoc and hold the old one
- if the user cancel the changes... It use the oldLoc to retrieve the initial cover