spam detector: custom rules: move apply/revert buttons to pending section

spam detector: custom rules: move apply/revert buttons to pending section

Move the buttons for applying or reverting pending changes into the
top bar of the pending changes diff panel, as then they are closer to
what they control and also only shown when relevant.

Drop the odd hint w.r.t. restarting pmg-smtp-filter from the top-bar,
as we can convey that better in the prompt, where there is already a
check-box that defaults to restarting that service.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>