GDISP changes including polygon support

Add polygon drawing
Add convex polygon filling
Start support for a monochrome display
Move gdisp doxygen to header file
Restructure the balance between gdisp.h and gdisp_lld.h
Remove old extern font definitions (now always use gdispOpenFont)
Make public the GDISP structure and change macros to suit (faster for
the application).
gdispQuery is now optional.
GWIN button changes

Support a user supplied custom button drawing function.
Add arrow buttons based on the new GDISP polygon support.