Draft: Fscan converter: add various fields

After discussion with ID15A staff:

>    - is the energy always stored in 1.1/instrument/positioners/llen ?
Yes, that's the pseudo motor for x-ray energy

>    - is the sample-distance distance always stored in 1.1/instrument/positioners/idx ?
Yes. This is not exactly the distance when using the KB mirrors but the error is negligible.

>    - is the approximate position of center of rotation always stored in the "hry" (pseudo-)motor ?
Yes: for half scans, the rotation stage and thus the rotation axis are displaced by the hry position w/r/t 0; for full scans hry~0. In both cases this is the starting guess to refine the CoR.

>    - where to find the optics magnification, to get the final pixel size ? x_pixel_size will only give the hardware pixel size.
The info is contained in 1.1/instrument/positioners/id2obj. A value close to -60.5 indicates the 20x objective and thus a 350 nm pixel size. A value close to zero indicates the 10x objective and a 700 nm pixel size.

>      - By the way, the metadata indicates "6.5 meters" for pixel size. Do you know if this is fixed ? This kind of issues makes any troubleshooting cumbersome
Maybe it comes from someone's attempt to input 650 nm (as the nominal pixel size with the 10x objective). It should be changed to the values in the answer above.