shell, NM model: Avoid accessing non-existent Settings field.
shell: Allow embedding of onoffbox in clickable areas.

By preventing the click event from bubbling up.
shell: Factor out set_slave function.
shell: Move network interface information around on the page

The active state is now included with the settings, and the interface
hardware is described in a single row.  This is in preparation for
adding the slaves in a later commit.
shell: Show network slaves on their masters page.