#52 Ability to set arbitrary outgoing headers

[Pete Verdon]

Specifically, I need to be able to set the Moderated: header (I have the
relevant permissions on my news server). Conceivably, other people might
need to set other things (including their own X-foo headers) so a general
mechanism for setting arbitrary headers would be better than special-
case Moderated: support. The Windows program XNews had this
behaviour.

Together with this, some sort of persistance so that I can specify
particular headers only once for the group that needs them (and not for
others) would be very useful.