Adapt web browser example to new web site.

- Change URL to qt.io.
- Save version number to settings and overwrite saved bookmarks
  unless version exists (enabling further updates depending on version).
- Save geometry and make initial geometry large to accommodate qt.io
  and High DPI screens.

Task-number: QTBUG-41798
Task-number: QTBUG-38858
Change-Id: I4da1d6e66135ff2867b6c678f5742767dbcb59fd
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>