Fix High Dpi Support. Works now under Windows and KDE/Plasma.

[hgraeber]

Commit 4a53082 was incomplete...

Qts scaling environment variables shall never be changed by application.
That way the user hasn't any chance to fix things himself. With setting
QT_AUTO_SCREEN_SCALE_FACTOR to 1 QtPass does not work under KDE/Plasma
and cannot even be fixed by setting Qts scaling environment variables.

[FiloSpaTeam]

I suggest this code:

#if QT_VERSION >= QT_VERSION_CHECK(5, 6, 0)
QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
#else
qputenv("QT_AUTO_SCREEN_SCALE_FACTOR", "1");
#endif

[hgraeber]

@FiloSpaTeam Why. The only reason can be that Qt 5.6s HighDPI is broken.

By forcing the QT_AUTO_SCALE_FACTOR environment variable to a fixed value you will break it even more, because it is not possible anymore to use the variable outside of QtPass to fix the behavior on some platform where HighDPI misbehaves.

So I can only repeat: It is better to never change those environment variables inside of the program.

[FiloSpaTeam]

https://doc.qt.io/qt-5/qt.html#ApplicationAttribute-enum

[FiloSpaTeam]

This is introduced in Qt 5.6 and Debian uses Qt 5.2/3 so they cannot compile.
Se have not defined a minimal Qt version so we should be compatible

[hgraeber]

@FiloSpaTeam With Qt before 5.6 HighDPI is broken anyways. For distributions using those old version I would expect that they patch it themself. I think they already have many other patches of this type inside of their packages and HighDPI still doesn't work completely right anyways.

[codecov]

Codecov Report

Merging #392 into master will increase coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #392      +/-   ##
=========================================
+ Coverage    6.49%   6.49%   +<.01%     
=========================================
  Files          39      39              
  Lines        2557    2556       -1     
=========================================
  Hits          166     166              
+ Misses       2391    2390       -1

Impacted Files	Coverage Δ
main/main.cpp	0% <ø> (ø)	⬆️

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[coveralls]

Coverage remained the same at 6.422% when pulling 59adb7c on hgraeber:master into 3f6f753 on IJHack:master.