freesound interim fix and clipart fix

CCBUG: 355350

 Fixes download of clip art.
 Fixes license parsing of clip art.
 Interim fix for search on freesound
 Freesound downloads high quality mp3 preview instead of the high quality file.
 This is because new freesound API needs you authenticate as user to get the high quality.
 There is a way to do it but I have not implemented this yet.
 Default file extension to mp3 on all freesound disable the import button while download is running -
 don't start two download jobs
 Fixes Auto play of previews in freesound.
 Preview button toggels on of the playing of the preview
 sound Preview button goes to "Stop" when playing preview and automatically back to "preview" when preview finishes
 Warns if you are about to overwrite an imported file I note that duplicate clip in bin checking is commented out in the code
 in ClipCreationDialog::createClipsCommand. And duplicate clips get created if you choose overwrite.
 Confirms the file download has finished.