Use Locale to determine time display format

This change deprecates the "ClockFormat" node for skins. Now we choose
the appropriate time format based on the set locale. Seconds can still
be shown.
Update resizable skins.

remove deprecated ClockFormat node.
Set default locale in MixxxMainWindow

Now we can use QLocale anywhere in mixxx and it will have the right
locale that was set at the start. This also allows now to revert all the
changes to the skinparser I made.
Start time with correct interval

I accidently removed the update calls -.-
Use systemLocale if no user selected locale is provided
Merge pull request #369 from kain88-de/use-locale-time

FIX: 1380091 Use locale time