Fix alt tab by not embedding blender window in qt

[hannesdelbeke]

this PR is the "final" PR that fixes the alt tab issues bqt caused, making blender absolutely useless.
without this IMO bqt is not production ready.

the alt tab issues happened when we wrapped blender in a qt window.
however, the main purpose of bqt is to support qt in blender.
this PR deliveres on that core promise, at the cost of removing wrapping the blender window.
this means that qt windows are not always on top.
but your qt app will work without requiring any special qt setup, and wont bug when alt tabbing.

an optional ENV variable let's you re-enable the window wrapping again. (which ofcourse re-introduces the alt tab bug)

it depends on previous PRs which should be merged in first.

• support qt5
• pass sys args to QApplication

[friedererdmann]

Hey Hannes, I'll try this PR locally, but maybe you can already answer: If the Blender window doesn't get wrapped in Qt, doesn't this create an issue with tool windows not staying attached/in the foreground of the Blender app?

[hannesdelbeke]

Hey Hannes, I'll try this PR locally, but maybe you can already answer: If the Blender window doesn't get wrapped in Qt, doesn't this create an issue with tool windows not staying attached/in the foreground of the Blender app?

indeed, as mentioned in the top post:

this means that qt windows are not always on top

But better to have a working blender, than a wrapped blender window that doesn't work

[hannesdelbeke]

adding the following enables you to hack your widget and always have it on top.
widget.setWindowFlags(QtCore.Qt.Tool | QtCore.Qt.WindowStaysOnTopHint)

note that without the tool flag the widget doesn't show up when using WindowStaysOnTopHint, so both flags are needed

[hannesdelbeke]

this PR has been replaced by #32
however it might be worth adding part of this PR to let the user chose if they want to embed blender in a qt window or not