Repair offspecular simulation in GUI (#641)

Previously, in !1593 (merged), I switched default units from degrees to q-space for all instruments.

But it turned out that q-units are not supported in off-specular mode.

So for offspec job the units have been reverted to degrees.

Resolves #641 (closed)

requested review from @j.wuttke

assigned to @m.svechnikov

approved this merge request

merged

mentioned in commit 7d4920a5