replace detector resolution example (#769)

Sharp diffraction pattern and exaggerated resolution function to show a clear effect.

Non-quadratic detector and anisotropic resolution to make test sensitive for bugs in index handling.

This resolves #769 (closed).

Follow-up issues:

• #772 (closed) revise ad-hoc repair of DiffUtil::meanRelVecDiff; investigate tiny numbers in examples/scatter2d/Resolution
• #773 (closed) update hugo