- removed src/buttons.c and include/BIF_buttons.h
- added src/buttons.txt, which is the old buttons.c for review and adding
code to new panels structure
- changed internal events to match new buttonspace structure
- added tabs for new shading group of buttons
- removed loads of little warnings, -Wall now compiles src/ almost without
error (hint: setenv NAN_QUIET to see it all better)
Now I'm ready to do actual buttons -> panels conversion. I will do the raw
versions first, others then can cleanup