Show a user's login methods on the user details page in the admin area

We have had a few people who can't login because they originally used a provider (e.g. GitHub), but are then trying to log in via another mechanism. This change shows a user's available login methods in the admin section, so we can easily point them in the right direction.
Possibly, although I think you may then need to put display properties into the `LoginMethod` class (i.e. css class for the icon, tooltips, order, etc...) to render it.