The Qt docs for 6.5 say that the minimum supported version is Windows 10
1809.
Experimentally it seems qutebrowser and it's dependencies work fine on a
version as early 1607.
There should be no change in OS version requirements for the Qt5 build,
although we've dropped 32 bit support already and in a future version of
the installer we may bring the minimum OS version support in line with
the Qt6 requirements for simplicity too.
Added a new QT5 version into the NSIS scripts so we can do the different
version check per installer build. It just uses the python bool
serialization format so should always be "True" or "False", but I've
added a fallback anyway for consistency.
f903ae4985