Group Admin: Updates to `bp_groups_admin_edit_metabox_members()`:

* Separate member roles and actions into option groups.
* Add a bit more intelligence to Ban action VS Banned role.
* Escape for JS and Gettext output where appropriate.
* General whitespace clean-up.

See #5645.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@8421 cdf35c40-ae34-48e0-9cc9-0c9da1808c22