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>
Merge branch 'feature/6742_maps_d4window' into develop