-title disappeared between Qt4 and Qt5, due to all the refactorings around QPA.
Making the caption of the mainwindow configurable allows custom setups
for specific users or use cases.
[ChangeLog][QtGui][QGuiApplication] Restore support for -title command line
argument on X11, add -qwindowtitle on all platforms.
Change-Id: I73e6bf21248f3419178eba583b257172a175e74e
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Reviewed-by: Albert Astals Cid <albert.astals@canonical.com>
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>