Make it a bit less painful to configure external (e.g. LDAP) authentication.

Squashed commit of the following:

commit 5136984c6211aa715b51e1108bcfc6c2838b6448
Author: Jeff Gehlbach <jeffg@opennms.org>
Date:   Wed Mar 5 11:43:13 2014 -0500

    Add some comments to clarify things a bit

commit 9f4d53078fc7360ff01e6b8e505249d8daeb11a4
Author: Jeff Gehlbach <jeffg@opennms.org>
Date:   Tue Mar 4 16:04:29 2014 -0500

    Blow up the external-auth stuff and provide some examples