Add a user detail view

I wanted to add a simple view where we could see the groups of a user.

This adds a user profile view listing all known information about them, plus the relevant user permissions.

It also allows a user to view a limited amount of information on other users, so it can act as an endpoint for user.get_absolute_url(), which may be nice at least for @carlespina's new workflow list view

This MR is best reviewed on a commit-by-commit basis