Bug fix for Issue 36 - "Preferences not saving".

Hi Gennadiy,
Here's a simple fix for Issue 36.

The problem originated in revision 8 of Jumpcut, which added use of NSUserDefaults without a call to NSUserDefaults's synchronize function on exit.  NSUserDefaults documentation states that synchronize is automatically invoked at periodic intervals but not automatically at exit and thus was unreliable without an explicit call.  The problem was masked by a call to synchronize whenever a clipping was added if save is enabled.

Thanks,
Mark