There are a few places in the system where this could be useful,
such as PixelPaint and the MandelBrot demo. It seems general enough
that it is probably useful to have it as a system-wide cursor rather
than loading it manually each time.
This can be used immediately in PixelPaint (separate commit), but
I am adding this as a system-wide cursor since it may also be useful
for other applications that want to use it.
