A human-readable "name" for every User

[mattyg]

Currently when User's are referenced in the UX, it is either by their Discord useraccount name, or their shortened ethereum address. This is determined by a utility function in the frontend.

I propose that we instead add a "name" field directly to the User model. When the associated useraccount is activated, the user name will be set to their first useraccount's name. Otherwise, the name will be set to some other value. Either a shortened version of their ethereum address, or a generated pseudonym based on their user._id.

It would also be ideal if every useraccount always had an associated user (see #361), and that user always had a standardized name, so that it could be easily referenced throughout the application.

We could then remove all the logic throughout the application which conditionally returns the UserAccount.name or shortened User.ethereumAddress depending on which data is available.