Limit the number of events that are filtered through a gesture recognizer

Most gesture recognizers are not interested in all event types, most of them are handling mouse and touch events (or possibly other user input events), hence we shouldn't even forward other event types to gesture recognizers.

The proposal is to add a property to QGestureRecognizer that specifies which event groups the recognizer is interested in:

enum EventGroup {
    AllEvents,
    MouseEvents,
    TouchEvents,
    KeyboardEvents,
};
class QGestureRecognizer {
    void setFilteredEventGroups(EventGroups events);
    EventGroups filteredEventGroups();
};