Add icons for admin actions

[marksweb]

Moderation admin actions display their links as text whereas all other apps (that I've seen) use icons now.

It'd be good to get some icons defined for moderation.

[fsbraun]

Just some ideas:

• Send for moderation:
  (send-check of bootstrap icons (svg freely avail))

• Approve:
  (shield-fill-check of bootstrap icons)