Simplify MailResponse class by not implementing smtp.IMessage.

We aren't using it as an SMTP message delivery class anywhere, so
there's no need to have the extra methods.

 * REMOVE bridgedb.email.server.MailResponse.lineReceived()
 * REMOVE bridgedb.email.server.MailResponse.eomReceived()
 * REMOVE bridgedb.email.server.MailResponse.connectionLost()
 * REMOVE zope.interface implementation declaration of
   twisted.mail.smtp.IMessage by b.e.s.MailResponse.
Simplify MailResponse by removing extra file I/O methods.

The only one we really need is MailResponse.close(), the utility methods
(i.e. MailResponse.rewind()) handle other important functionality for
us.

 * REMOVE bridgedb.email.server.MailResponse.flush()
 * REMOVE bridgedb.email.server.MailResponse.read()
 * REMOVE bridgedb.email.server.MailResponse.readline()
 * REMOVE bridgedb.email.server.MailResponse.readlines()
 * REMOVE bridgedb.email.server.MailResponse.seek()
 * REMOVE bridgedb.email.server.MailResponse.tell()
 * REMOVE bridgedb.email.server.MailResponse.truncate()
Fix bug in MailResponse.write() multiline string handling.

The bridgedb.email.server.MailResponse.write() method wasn't properly
converting '\n' newlines in multiline strings to SMTP-formatted '\r\n'
newlines.

 * FIXES multiline string newline replacement bug in
   bridgedb.email.server.MailResponse.write() method.
Fix misnamed methods in MailMessage.reply() docstring.