Don't use is_super_admin() to die out of group/activity admin pages

Use current_user_can( 'bp_moderate' ) instead.

This gives more flexibility in customizing who can access.

Fixes #5177

Props asakurayoh for the initial patch

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7387 cdf35c40-ae34-48e0-9cc9-0c9da1808c22