Restore colors manually

Hi Pierre,

 I've made a couple of changes to your Restore_colors script as requested on our forums https://www.openmicroscopy.org/community/viewtopic.php?f=4&t=7431.
These should make it generally useful for users with other types of data, by adding a parameter for manually choosing the colors.

Also, I've added "Plate" as a data type and made a couple of fixes so that the script handles a large number of images.

I've opened this PR so you can merge these changes back into your branch IF you want to, but this is completely optional. I'll refer to this PR from the forums, so the user will be able to grab the script from here regardless of what you choose to do.

 Regards, Will.