Refactor IPersonManager implementations slightly to avoid unnecessary bean tweaking to enable RemoteUserPersonManager

uPortal supports several flavors of authentication with RemoteUserSecurityContext, including Shibboleth & CoSign.

Currently...

• If you're using RemoteUserSecurityContext, you must also use RemoteUserPersonManager

• To enable RemoteUserPersonManager (in uP5), you must overlay userContext.xml

That's not great – we're hoping to avoid overlaying Spring XML config files in all cases, or at least to the greatest extent we can.

Refactoring the class hierarchy of IPersonManager slightly will allow us to define a standard bean (that implements IPersonManager) that also works with all flavors of authentication.