Invert a set with quartering

Hi,

Added the possibility to use quarters when you are doing "invert a set". Looks like you had written the code to do it but wasn't set up.

quarters 1234, just like in the "quarter button". "0" is using the whole image as normal.

I have changed the filenames output from what you originally designed. It creates some extra folders to keep things tidy and record which centre you used for the inversion.

Ciarán