Testing MultiWedge to segment galaxy pixels

By directly segmenting against galaxy pixels it becomes possible to
segment an image into several wedges, covering all position angles.
Got PA image to be properly oriented
Refactor pixel mapping of R and PA
Segmentation image in de-projected PA

But... actually I'd rather bin in PA projected on the sky!
Compute PA in sky
Build a full radial + PA segmap

TODO:

1. There seems to be an angle offset in the first wedge along the major
axis
2. Set pixels beyond the radius grid to nan in the segmap
3. Make a table of pixel IDs and their R, PA values
4. Make the first bin of the major axis wedge a ellipse that covers all
PAs
Make central elliptical bin
Leave pixels beyond the radial grid blank