Automatically remove rejected sessions from review page, those with enough rejections, to avoid effort waste with ineligible sessions

[pablobender]

The review page, at moment, list remaining sessions to review by the current reviewer user.

The application would remove the sessions with enough rejections to discard the session from the grade.

[] check if the 2 rejections is a manual rule, a configuration in the application or even if it can be configured in each conference
[] remove the rejected sessions from the list of sessions to be reviewed.
[] list number of remaining sessions and the "rejected sessions"
[] allow to list/filter "rejected sessions"

[pablobender]

duplication of #274