Polish the webbrowser example.

Update address edit when the browser finishes loading.
Add some rudimentary bookmark/history functionality. Add relevant
default bookmarks and make qt-project.org the start page.
Handle URLs passed on the command line.

Change-Id: I21efeb5b4d2a05941407d308a96df7b024100f19
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>