Use QMessageBox::Cancel for cancel buttons
Fix spelling in comment
change default skin to LateNight
Merge pull request #353 from kain88-de/change-default-skin

change default skin to LateNight
Fix master sync edge case.

Make sure reported beat distances are adjusted to account
for the user offset.
Merge branch 'master' of https://github.com/mixxxdj/mixxx into coverArtSupport
adding the CoverArt widget to the LateNight skin