- replace use uniformly Gui::QuantitySpinBox
- fix and uniform size of all objects in the dialog
- apply changes immediately once the section is created because this speeds up the workflow a lot, especially for when changing the plane position
- some code cleanup: remove unused void, avoid unused variables
- if the Section is deleted while the section dialog
is still in progress, further processing in the
dialog would cause a crash.
- should have "update intent" locks to prevent this
