Allow unregistered users see visible-but-awaiting sessions

[damithc]

Context: Although rare, TEAMMATES allows a session become visible to respondents before the submission time. The purpose of this is to let respondents see the questions ahead of time.

Current: Only registered users can see such sessions.

To let unregistered users see such visible-but-awaiting sessions, TEAMMATES will need to send an email to each respondent when a session becomes visible, if it is earlier than the opening time.

Discussion: cost vs benefit, implementation effort. One extreme solution (if cost >> benefit) is to remove 'visible time' altogether i.e., instructors will have to use some other means to educate respondents about the session questions ahead of the submission opening time