webengine

to prevent the overscroll bounce effect, need this css:
```
body {
  overscroll-behavior: none;
}
```
on mac, modifiers are not as expected:
- command key produces control modifier
- control key produces meta modifier
- alt key produces ...

to get events from the webengine, need a workaround

def childEvent(self, event: 'QChildEvent') -> None:
    # This is a workaround for https://bugreports.qt.io/browse/QTBUG-43602
    # We need to grab events from a child of the web engine view - normal
    # method overrides do not work
    if event.added():
        event.child().installEventFilter(self)