pass current document to views, so they work on this document, not with global pointers and MainWindow

...instead via MainWindow

...instead of access via mainWindow

...instead of access via mainWindow

because it makes problems with height-for-width contents like a label with wordwrapping

use radio buttons instead of comboboxes for 2-choice-options; fix missing update on project load; add missing "document modified" after editing; refine UI

...this info is contained in the details pane as well

also rm now obsolete code

more simplifications; put method docu on one place only; rm unused include; fix uppercase of include

replace GUI::Project::Utils::userExportDir() by GUI::Project::Manager::userExportDir() (unnecessary indirection)

Rename functions to be consistent with other names and add new functions needed by upcoming changes.