GUI: migration from SessionItemWidget, part 2

Migration of plotting widgets from SessionItemWidget to DataAccessWidget is done. Some cleanup and bug fixes after this transition will be added in the next MR.

Some classes were deleted here.

• Since RealDataMaskWidget class was almost empty and just contained MaskEditor, I moved functionality of MaskEditor to RealDataMaskWidget. MaskEditor was deleted to diminish the number of such "layers".

• The same about ProjectionsEditor: its functionality was moved to IntensityDataProjectionsWidget, ProjectionsEditor was deleted.

• FitComparisonController, FitComparison1DViewController, Plot1D, Plot1DCanvas, DataItemUtils became completely deprecated and so they were deleted.

Note:

MaskGraphicsScene.cpp has a function MaskGraphicsScene::onSceneSelectionChanged() with commented out body and reference to issue 319. This is a temporary action, in the end of this refactoring, in next MR, the bug is gone and this function is back.