[aprssig] Vicinity plotting

[Bob Bruninga]

> I think I'll make vicinity plotting optionally enableable 
> but off by default, and stop reporting anything as 
> distance-to-station for Coast-of-Africa points.

If it is off then they will never know it is there.  I think it should be on
by default and when all those big QUESTION MARK symbols show around the
digis (without callsigns) then let them wonder what they are and discover
that they are vicinity plots.  If they don't like them, then they can turn
them off.

> Bob doesn't agree with the way I do it, but I render it 
> 1/2 across the ambiguous position, draw a tight purple 
> circle around the symbol to indicate that something is 
> strange here, and (if enabled by the user)
> draw a large circle at the ambiguity distance.

Again, Id prefer to see the full size circle by default so that they learn
what it is, and then they can turn it off when they understand ambiguity
plotting.

My 2 cents.
Bob, Wb4APR