Doc: Fixed a few broken links and snippets

Couple of \snippet references in the ListModel docs
were pointing to files outside the exampledirs boundary.
Update those references to use the relative path.

Change-Id: Ibf9d0fda9e5280345b08cb66a4fe0db9142a42a6
Reviewed-by: Nico Vertriest <nico.vertriest@digia.com>
Reviewed-by: Topi Reiniö <topi.reinio@digia.com>
systemdialogs example: path to /tmp is different on Windows

Task-number: QTBUG-34100
Change-Id: Ic06ed2933b76704b1a298de826cbe6b8587fee76
Reviewed-by: Jan Arve Sæther <jan-arve.saether@digia.com>