Fix Colocalisation_Test window crash on multiple runs

[pvlaraia]

Summary: If a script uses Colocalisation_Test, and closes the result window, subsequent attempts to run Colocalisation_Test will crash because the reference to the window will still be there, but the attempts to write to the window will crash because the window was closed. To verify, revert changes to Colocalisation_Test.java & run the new test case added - the 2nd attempt to run coloc in the unit test will fail.

The solution was to cleanup the window ref when a window is closed.

[pvlaraia]

@ctrueden I see you've been involved in a lot of the most recent commits, is this something you could consider merging in?

[ctrueden]

@pvlaraia Thanks for the ping. I'll try to review and merge it this week.