GUI: wavelength is back to specular teal time tree

The wavelength is returned to real time parameter tree for specular scan.

But, according to the issue #301 (closed), there should also be changeable "Inclination angle" which is a scan parameter.

The reference to this issue is added to the code.

changed milestone to %21 GUI fixes

added GUI label

requested review from @j.wuttke

assigned to @m.svechnikov

approved this merge request

mentioned in commit 4a714e16

merged