Update core committer information on the staff client's About Page

senator has not contributed anything new for the past six months and is
therefore moved to the "Past Core Committer" listing per policies on:
http://wiki.evergreen-ils.org/doku.php?id=contributing:contributors

berick belongs to a new organization and this has been updated accordingly.

Signed-off-by: Ben Shum <bshum@biblio.org>