gui settings: add 1x1 only to repetition VA, not resolution

1x1 is handy for allowing scanning just a point (on the SPARC).

However, setting up the CCD or SEM resolution to 1x1 is useless, so remove it
from the GUI by default (it's still possible for the user to get it by manually typing it).
gui model: reduce maximum mpp allowed for a view

This means in practical terms that the maximum HFW is about 20mm in the small window.
That should fit any kind of microscopy sample. No need to allow up to a meter.