driver pigcs: fix bug handling empty lines from IP controller

If the IP controller only return \n (which it shouldn't, but seems to happen), then
a IndexError would trigger when looking for the non-existing space.

Handle such a case.
acq mng: really fix FluoStream ordering

also handle the case of multi-band filter.
gui settings: fix radio button not linked to the right value

If choices is a set (or a dict), it will not have any order, so we cannot rely on it.

That's why choices_fmt contains both original values, and formatted value. => use it.

Also fix missing unit prefix.

All these were noticable on the readout rate of the fake andorcam2.
gui: support backscattered electron detector

Prefer SE if both detectors are available.

This allows to have the Delphi report correctly that the SEM uses backscattered electron detector.

This should also (in the future) allow to support SEMs with both SE and BSE detectors.
config: update Delphi microscope file to correctly report backscattered electron detector

now that the GUI supports correctly BSED, let's use it.