Added ability to define a 'target time' for levels which is taken into consideration...

Added ability to define a 'target time' for levels which is taken into consideration when marking a level 'perfect'.
As a proof of principle, Icy Island levels prior to the underground sequence have been assigned arbitrary but attainable target times.  However, this feature probably should only be used with great care in the main game (if at all).  Statistics still need to be modified to display the target time if defined, otherwise it will be confusing to players trying for perfet stats.