Fix a memory leak

For some reason, Coloc_2 having an inner class WindowAdapter instance
resulted in some object reference hierarchy which prevented garbage
collection of the Coloc_2 (as reported by a JVisualVM heap dump).

Explicitly unregistering the WindowAdapter upon window closing fixes the
issue, so that garbage collection purges all the Coloc-2-related objects

• in particular, the SpearmanRankCorrelation double array fields, which

are essentially complete copies of the images.