- refactor register_settings to allow lookup by GType and
  add the settings name to SettingInfo.

- setting NM_SETTING_NAME is deprecated and should not be set anymore.
  Indeed it has always be a bug, to reset the name to a different value.
  The only valid place to set the name was in the _init() function of
  the derived class itself.
  This is now no longer needed/possible. Instead the name get's
  detected based on the registered setting types. This makes use of
  the registered metadata that is available anyway since every
  usable setting has to register itself.

Signed-off-by: Thomas Haller <thaller@redhat.com>