Recreate subtraction images to fix DATE-OBS and DATE-END times in header

[jburkepile]

The new 2.2 release of K-Cor subtractions has the background image time in 'DATE-OBS'. This is incorrect and needs to be changed to have the foreground image time in 'DATE-OBS'. Users reading in the DATE-OBS time to create CME trajectories will be off by 10 minutes, since the nominal time of the background image is 10 minutes earlier than the foreground (CME) image. The background image time is already captured in the 'avgtime' keyword in the header.

FYI: Mike ran the older version of the subtraction code (code with 5 minute cadence) to check what time was in 'DATE-OBS'. The older code did properly record the foreground (CME) image time in DATE-OBS.