Allow external users

[hackartisan]

Their uid and username are both their email address. princeton.edu is no
longer appended to make the email address if the uid is already an email address.

This should be deployed to staging and tested.

progresses #750

[coveralls]

Coverage remained the same at 100.0% when pulling 0498628 on 750-external-users into 977c59b on master.

[hackartisan]

I tested this fix on staging and it works for a general case. I couldn't figure out how to "invite" a user so I didn't test that functionality.

[kelea99]

@HackMasterA I invite a user simply by adding them to a collection and letting them know about their collection. I wonder if there is a better way?

[hackartisan]

@kelea99 that's the process I've tested, and I think it works fine. The code has a concept of a "pending invitation" but I'm not sure how that manifests in UI. @tpendragon any idea?

But I think the test should suffice to ensure it's working okay and also that if we're not using this feature we don't need to worry about it too much.

[tpendragon]

No, I'm not sure. I think that's a Spotlight system that we just kind of ignored?

[kelea99]

sounds good to me, @HackMasterA. Im so glad its working in staging! When you are ready, just let me know and Ill contact the collection owner to give it a try. Thank you!!