GUI: fix handling of a new real data

Mikhail Svechnikovrequested to merge
fix_mask into main

The MR fixes two things:

  1. prevents executing setContext() method in IntensityDataProjectionsWidget and RealDataMaskWidget. This happens when deleting existing data and then importing new one.
  2. for newly imported data the default presentation is set. Previously the last used presentation was applied.

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