E-mail sever only login once & UiO server settings.

Rewriting of the e-mail server login / out structure.  Additiation is
new class `SMTPUiO` and `SMTPGoogle` which are both subclasses of email
server class meant for for holding e-mail server connection which must
be given when initializing an `Email` instance.  This also gives
functionality for sending from a UiO e-mail address. New command-line
argument `smtp` lets user choose which server. UiO server takes both
e-mail adress for e-mail envelope and username for logging in.

This solves problem where server had to keep logging in / out for each
e-mail sent.
Added logout method to Email class.
Removed test_uio_email function.
smtp.quit instead of smtp.close
Merge branch 'master' of github.com:hplgit/virtual-classroom

Conflicts:
	src/start_group.py
Fixed bug: From e-mail correctly fetched from server connection.
More from fields not fetching correct from e-mail.
Merge pull request #3 from benedicteb/master

Ikke logge av / på epostserver. Mulighet for UiO smtpserver.