Add sortable column support for the Groups Administration Dashboard panel

The columns have been marked sortable since they were originall introduced, but
the sorting did not work because of limitations in how bp_has_groups() worked.
As of r7087, bp_has_groups() supports 'order' and 'orderby' params, which
allows us to fix this broken feature.

Fixes #4483

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7088 cdf35c40-ae34-48e0-9cc9-0c9da1808c22
POT, generated from r7088

git-svn-id: https://buddypress.svn.wordpress.org/trunk@7089 cdf35c40-ae34-48e0-9cc9-0c9da1808c22