We now use click() or focus() in JS if possible, or manually follow links in a
href attribute.
While this probably introduces some new corner cases, it fixes a handful of
older ones:
- window.open() in JS can now be handled correctly as we don't need hacks in
createWindow anymore.
- Focusing input fields with images now works - fixes#1613, #1879
- Hinting now works better on QtWebEngine with Qt 5.8 - fixes#2273
Also see #70.
