Fix the following warning from Qt 5.14.1:
error: ‘static QList<T> QList<T>::fromSet(const QSet<T>&) [with T = QString]’ is deprecated: Use QList<T>(set.begin(), set.end()) instead. [-Werror=deprecated-declarations]
Regarding QList::fromSet(), the documentation now states the
following [1]:
Since Qt 5.14, range constructors are available for Qt's generic
container classes and should be used in place of this method.
[1] https://doc.qt.io/qt-5/qlist.html
In particular, the directory frontends/qt4 is renamed to frontends/qt.
Many configurations file have to be updated. All mentions of qt4 in
the source have been audited, and changed to qt if necessary.
The only part that has not been updated is the CMake build system.
