LP 1890629: Make Self-Registration Opt-in Settings Lookup Tree Aware

LP 1890629: Make Self-Registration Opt-in Settings Lookup Tree Aware

Patron self-registration in the OPAC only shows the opt-in settings if
the events are owned specifically at one of the locations where patron
self-registration is also allowed.  The event could be owned higher up
the org. tree from the libraries that allow self-registration,
particularly in a consortium where not all members do
self-registration.  This patch changes the search for opt-in events to
include the ancestor org. units of those that allow self-registration.

Signed-off-by: Jason Stephenson <jason@sigio.com>