Reviewer Management: Current number of open reviews must display the number of open reviews for that reviewer and not for the challenge

[jmgasper]

REF: https://topcoder.atlassian.net/browse/PM-933

Reviewer Management: Current number of open reviews must display the number of open reviews for that reviewer and not for the challenge.

After discussing with QA, let's just rename the column as Open Reviews to avoid confusion.

[phead198708]

Ready for review: #1053

[jmgasper]

@phead198708 - The text needs to be Open Reviews, not Open Review. I've fixed this, but having the required text is important, thanks.