Material refactoring

• reduce SessionModel exposure
• reduce SessionModel usage
• avoid global access to material model
• minor changes

added GUI cleanup simplify labels

requested review from @j.wuttke

added 2 commits

• 2f690fd5 - make const
• b7ba9971 - refactor to avoid usage of global access to material model (OOD)

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added 1 commit

• f09dabf6 - use curr doc instead of global access to material model

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changed the description

approved this merge request

ok

mentioned in commit b9005e44

merged