Improve sample and materials handling in GUI

From the recent discussion and application of BA GUI to model "lipid bilayer on Si crystal with SiO2 nanoparticles"

• show material name for particles
• hide magnetization by default as it can be easily confused with the particle offset
• allow shell offset in Core-Shell model
• automatically suggest e-06 for the new materials, for example in a separate spinbox
• review truncation parameters: UntruncatedHeight, Delta height, Height flattening are unclear to the user. Maybe just Top cut, Bottom cut, Horizontal radius, Vertical radius?
• ease distingushing particle groupboxes from each other. Slightly change color, assign name?
• Interference function None: replace with Disorder or Random

changed milestone to %v22

added GUI inconvenient UI user request labels

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assigned to @m.svechnikov

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marked the checklist item Interference function None: replace with Disorder or Random as completed

mentioned in merge request !2908 (merged)

marked the checklist item hide magnetization by default as it can be easily confused with the particle offset as completed

mentioned in commit 1aaf1c4b

mentioned in merge request !2909 (merged)

marked the checklist item show material name for particles as completed

changed the description

mentioned in commit a547f8ef

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mentioned in merge request !2910 (merged)

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