Refs #0

While helping prepare an article, I ended up deriving the equivalence of
delta-d/d = delta-T/T. Since it wasn't a 5-second derivation, it seemed
a good thing to add to the user docs.

This split out the material information into a new concept page, added
additional links between the various docs, and added a big note at the
top of `SetSample` that the dict definitions are in cm.

Refs #23399

Problem identified: sample log entries are not case sensitive. title, Title will not result in different SampleLog entries

Refs #24312

Refs #24312

I think it is more appropriate to ask for title (a SampleLog entry) and not Title (the parameter name in the file)

The fix:
Title was not recognized as existing header component and repeated.

Refs #24312

Refs #24321

Replace references to PyEpics now it is replaced with CaChannel

The algorithm was assuming too much about the input workspace's
detectors resulting in too large theta width for ILL's IN4 and
IN6 instruments. Also, the algorithm expected a constant L2 for all
detectors which is not true for IN5. Further, picking the first detector
only for the theta width calculation was not sufficient for cases like the
detector groups in the workspace used in the unit tests.

We now calculate top, centre and bottom points of the detector's
bounding box, apply rotation and translation taking the sample position
into account, and calculate the 2theta angle between the points and the
beam direction. This is repeated for all detectors in a group. The final
theta width is the difference between all thetas calculated.

Additionally:
- Remove phi angle stuff, it is not needed for anything.
- General cleanup and refactoring.

Re #24041

And also updated doc for the new bindary file format.