Bug: a88/8c7

It seems relatively common to have North on the positive Z axis
on a Zplot (see e.g. Dunlop 1979, Wilson and Roberts 1999). Dunlop
recommends making the x axis the intersection between the vertical
projection plane and the horizontal plane. Nobody's asked for this
at Otago but it seems common enough that I should implement it
before wider release.

This isn't particularly difficult, but due to severe time pressure
for the 1.0 release, I'm going to defer it to 1.1

Bumping up to 1.03 since someone's finally requested it.
JMG writes:
It would help visually if you lined up the common axes on the
Zijderveld diagrams

A plan for implementation: currently the Zplot is two overlaid
plots: a fixed horizontal plot with North always at the top,
and a vertical plot which always has Up at the top but has three
options for the horizontal axis (N/S, E/W, H). For now at least
I think the vertical-plot options are sufficient; maybe there are
occasions when you'd want Up at the bottom, or an inverted hz
axis on the vertical plot (N->S or E->W rather than S->N or W->E).
But I don't remember seeing these conventions used anywhere, so
I'll wait for someone to request them specifically. The thing we
definitely need is one more option for the currently fixed 
horizontal plot: west at the top and north at the right, to line
up the S->N axis with the corresponding vertical plot. So this
can actually be implemented independently of the existing
vertical-plot options, maintaining backwards compatibility of
preferences files, and with minimal changes to the existing UI.
Easiest would be just to add an option to the Preferences window,
though this makes it a bit of a pain for people who want to 
switch quickly between N,U/E,E and W,U/N,N plots. But maybe it
will suffice for a stopgap, since in the long term I want to
re-design the preferences/plots system anyway.

I'm reducing the scope of this issue to just implementing
"west-upward" horizontal projections. I've opened a new ticket 
(a88/9c82 Full control over Zplot projection planes) for a more
complete implementation.