Set QStyle::State_Active conditional to whether the window is active,
which maps to Qt's active window concept and winit's has-focus (until we
render popups differently).
When the window is mapped, the scale factor is brought up-to-date. Only
after that we can receive a resize event or a window scale factor
changed event.
Under these windowing systems, we receive a QString text from Qt that
contains a terminal control character (like \u{3} for ctrl+c). We
decided to supply the character for the key (for example 'c' for Ctrl+C)
to the application, so activate the conversion from the key code when
control characters are present.
With winit, we receive first a key down input event with the virtual key
code (for example C for Ctrl+C), followed by a ReceivedCharacter event
with a terminal control character. We choose to ignore that and instead
take the previously received key code and try to use that instead.
Fixes#441
