FormFactor to Python: minor edits

See merge request !292

Small cleanups

See merge request !291

Refactor Application Models

See merge request !290

and adapt unit tests

...instead of MainWindow

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

Refactor model access

See merge request !289

...instead via MainWindow

...instead of access via mainWindow

...instead of access via mainWindow

...instead of access via mainWindow

small UI refactor

See merge request !288

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

change to instrument view after opening a project

See merge request !287

Project handling

See merge request !286