Introduces new hook - "bp_groups_admin_manage_member_row"

On the "Groups" dashboard, in the "Manage Members" metabox, add a new table
row so plugins can inject additional information for each group member.

This table row is only rendered if a plugin is using this hook.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@6959 cdf35c40-ae34-48e0-9cc9-0c9da1808c22