-1-7-3 multi-users

-add support for different users have different query results at only
one instance. (Before, if two users query at the same time, their query
result will affect with each other)

- update database, now, different users have their own email list in
database. In this way, different users can manage their  alerts on
thier own page.

- add email black list support. if one google user is added, he cannot
use course notifier. Only can use as a public user.