added uc_uid mapping to shibboleth authentication

[thecoolestguy]

Some institutions require comparison to an authentication field other than email address. I've added the institution id (uc_uid) field as an option as it is the probably the next most in-demand to the email address.

[jrjohnson]

I'm ok with this if it fixes the problem right now, however my understanding of shibboleth is that the eppn (Edu personal principal something) is supposed to be the primary unique identifier for authentication. I think if we're going to add the option to pick your auth method it should include that attribute.

[jrjohnson]

Never mind - I see that if I set it to uc_uid and store the eppn there I can then set the ilios_authentication_shibboleth_user_id_attribute to eppn and that will do it.