Allow detectors to be numbered in reverse order in a tube re #6742

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Deal with detectors in reverse order without reversing tube re #6742

This also fixes the problem of the tubes sloping.

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Tidy up python code re #6742

This commit was needed only because I made the previous one without saving.

Signed-off-by: Karl Palmen <karl.palmen@stfc.ac.uk>
Merge remote-tracking branch 'origin/feature/6742_maps_d4window'