Added email field to user table.
Added email field to user table.

References #289.

agdsn/pycroft,lukasjuhrich/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,agdsn/pycroft,agdsn/pycroft,lukasjuhrich/pycroft,agdsn/pycroft,lukasjuhrich/pycroft