add default/customizingCss action to op_ssl_selectable_actions (fixes #3500, BP from #3475)

(cherry picked from commit 21d2d6d43741c72b82d4ffca86a96525c15d9ed7)
revoke automatic login cookie before registration (fixes #3498, BP from #3416)

(cherry picked from commit 2cac338f0edd68b57d534413e54d4b4380237a83)
use empty string to clear member cache (fixes #3498, BP from #3416)

(cherry picked from commit eb5fe39f5619e7bcac973ca61bd32a94bfa28090)