Use QT_DEVICE_PIXEL_RATIO=auto on Qt<=5.5 to enable automatic
scale factor settings on Windows. Also move the existing
Qt::AA_EnableHighDpiScaling logic to use the equivalent
QT_AUTO_SCREEN_SCALE_FACTOR=1 environment variable just to
keep the 5.5 and >=5.6 code at the same place.
This moves the crash handler installation during the OCC::Application
contruction. This still leaves a window where crashes wouldn't be
caught, leaving the QtSingleApplication and theme initialization
code unreported, but isn't requiring any refactoring for now.
Issue #2952
The config currently only disable the reporter, but still leaves
the crash handler installed on startup. This causes conflicts
when running those builds in lldb.
Work around the issue by requiring the crash reporter to be
disabled in the settings before owncloud can be run in lldb.
This has the negative side-effect of not covering the
initial ConfigFile loading with the crash handler.
Issue #2946
sendMessage would only be called if there were options to
be sent to the running application.
Fix the issue by having explicitly named messages and always
send the show settings message.
Issue #2374
