fix project reading error introduced with global renaming of "OffSpecInstrument"

See merge request !83

fix project reading error introduced with global renaming "OffSpecInstrument" -> "OffSpecularInstrument"

Refactor model: SymmetricDistributionItem

See merge request !82

Refactorings no. 2 for the upcoming removing of "region of interest" (ROI)

See merge request !81

add unit tests as well

necessary for later refactoring

was not in use at all, only in tests. Only roiIndex and detectorIndex shall be used

* remove indirection class SimulationArea
* docu
* adapt tests

Remove unnecessary includes; remove dependency of error reporting on main window

See merge request !80

Refactor for removing RegionOfInterest

See merge request !79

the call is contained in the following call to isMasked()

Refactor model: DistributionItem

See merge request !78

Refactor model: BeamDistributionItem

See merge request !75

Fix crash in selecting "Masks" after 2D data import from combo box

Closes #81

See merge request !77

Refactor model: SpecularBeamInclinationItem

See merge request !74

CMake improvements

See merge request !73