* pf_safety/start.ph: In addition to having a gatekeeper() call in the
  page handler, remove the menu item for this plugin from the site
  menu bar if the visitor isn't logged in.
* pf_safety/start.php: Handle groups and river in the same manner as
  members.  Enhance the comments a bit.

* pf_safety/manifest.xml: Add dependency on groups.  Add license
  information.  Bump version to 0.5.