* QString::indexOf() is now marked as [[nodiscard]]
* Replace deprecated methods of QMessageBox
* QMouseEvent::globalPos() is deprecated, use globalPosition().toPoint()
* QWidget::enterEvent() requires a QEnterEvent as argument
* QLibraryInfo::location() is deprecated, use path()
* QVariant::Type is deprecated, use QMetaType::Type
* QVariant::canConvert(int) is deprecated, use QVariant::canConvert(QMetaType) or QVariant::canConvert<T>()
* QMessageBox::standardIcon is deprecated, use QStyle::standardIcon()
* Replace deprecated method QMessageBox::question(), ...
* QApplication::fontMetrics() is deprecated
* QDropEvent::mouseButtons() is deprecated, use buttons()
* QDropEvent::keyboardModifiers() is deprecated, use modifiers()
* Constructor of QFontDatabase is deprecated, use static methods instead
* Qt::AA_DisableHighDpiScaling is deprecated
* Qt::AA_EnableHighDpiScaling is deprecated
* Qt::AA_UseHighDpiPixmaps is deprecated
* On lines where the variable type is obvious from inspection, avoid repeating the type using auto.
* When possible use a ranged for loop instead of begin() and end() iterators
This patch includes the actual implementation of Link, which is
implemented as an extension named LinkBaseExtension in App namespace,
and a full view provider ViewProviderLink in Gui. The reason of not
using ViewProviderExtension is because it need full control when
display, not just extending existing functionalities.
Please see [here](https://git.io/fjPue) for more details of the
implementation.
This patch also includes a set of link manipulation commands, and a
task panel for overriding geometry element colors.
