New Astropy coordinate patches and SunPy coordinate support

I don't know if you want the SunPy stuff hard coded in Ginga, but it shouldn't cause you any issues.

I have also done some tweaks which make more use of SkyCoord and the new coordinates framework. The list of available WCS coords is now populated from the transform graph. Also in a bit of a weird hack, I removed any Frame dependency on the SkyCoord attribute access.