GUI: make data storing in DataItemBundleWidget more explicit

Mikhail Svechnikovrequested to merge
i362b into main

After fixing #362 (closed) here is a simplification of DataItemBundleWidget class.

Now it stores IntensityDataItem* and vector of SpecularDataItem* without any type conversions but does some nullptr checks.

Edited by Mikhail Svechnikov

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