Adding springboard social paths to admin_paths

This addresses a bug with springboard social where the social settings page for individual nodes does not receive the admin theme when the "use admin theme when editing content" Appearance option is selected.

There are relevant tickets on two projects:
https://www.assembla.com/spaces/sb4-admin-ui/tickets/806#/activity/ticket:
https://www.assembla.com/spaces/dga/tickets/59#/activity/ticket: