further corrections suggested by clang-tidy

See merge request !453

Fix crash in model view ("tech view")

Closes #141

See merge request !452

various little improvements as suggested by clang-tidy

See merge request !451

rectify parent widgets

See merge request !450

For dialogs it is dangerous and sometimes directly causing errors if their parent is an arbitrary widget (like e.g. a button or an embedded form)

Minor corrections (from threads in MR 447)

See merge request !449

Fix/improve global settings

See merge request !448