Import the demo browser into widget examples.

Import the sources as-is, without adding it to the build, to allow
performing diffs later on the changes that were needed to port it
to use QtWebEngine and manage source compatibility issues.

Change-Id: Icf8a284881ce2153e9b5a1ba97dbe77096f1b88d
Reviewed-by: Andras Becsi <andras.becsi@digia.com>