cherry-pick 'fix_stitching' into 'master'

Fix stitching

See merge request !410 (merged)

(cherry picked from commit bc22b574)

d12c4090 stithcing: update doc 21d971a5 stitching app: improve robustness in case is simply a file like 'output.nx' e2aceac6 StitchingConfiguration: use modules instead of python script