checkpoint.  removing XF-specific parts of crossgraphics.  moving back closer to the crossgraphics I started with, except some changes do still need to be ported back over.  added DataGrid.CrossGraphics project.  moved Graphics.cs in there.  and the DrawCell classes also (from dg_xf_grid).  AndroidGraphics and CoreGraphicsGraphics moved into projects that are android/ios specific but which do not have a reference to XF.  some things currently broken.  work in progress.
fix android and ios graphics with changes from previous incarnation.  font handling is a temporary hack at the lowest level, because CrossGraphics.Font doesn't have handy converters to platform fonts like Xamarin.Forms.Font did.
notes