When an invite is sent to me, it should show up in my Notifications

(Incomplete Feature, Investigate , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Invites
Summary: Currently, invitations are only sent via email. But they ought to be visible when I log in.
Pointed out by Aaron.
Fixing this potentially cleans up the stack nicely -- it removes a special-case route that goes directly to email. But it requires that we have notification-to-email implemented first, and it needs to be able to cope with invites to non-members.