added warning to check whether a night has been done

If a worksheet corresponding to a night is found, the script now prompts the user to check whether the night has already been looked at
fixed a bug and added more tests

xbin and ybin were not being tested correctly. Started on CCD tests
MCCD no longer a subclass of list, added reverse arithematic operators

Quite a few changes. Can now add constants to CCDs and MCCDs, not just other CCD and MCCDs. Window supports statements like "10+win" now