#13 Impersonation of user by administrator

[adam marshall]

It would be good to have a button which when pressed
allows a tutor to impersonate a user from a given group
(or possibly a user in a set of given groups). This
would allow 'tutors' to see what Bodington looks like
for their tutees.

Impersonation would terminate withthe end of the
session or when another 'stop impersonating' button
were pressed.