Change URL of Nokia/HERE developer website.

The Nokia geo services are undergoing a branding change and is now known
as HERE. Change the URL printed when the required app_id and token are
missing from the plugin parameters. It is no longer obvious how to
register for application credentials at the previous URL.

Change-Id: I50dcd428fd690705b802d5cf6090b0a800ea0622
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>