Replaces QStringLiteral by QLatin1String

QStringLiteral was introduced in Qt5.

Change-Id: Id1942225a1a9758db7bc8e05df45223d13bf86dc
Signed-off-by: Luís Pereira <luis.artur.pereira@gmail.com>
Reviewed-by: David Faure (KDE) <faure@kde.org>