This just provides some nice visual feedback when you are in the
middle of selecting a color. An eyedropper might not be the ideal
choice here, but among the cursors we already have it is the
best one.
Now we add a little marker to show the current sample position of
the CloneTool. The current implementation for updating the cursor
location is really dumb since it just updates the whole editor,
but that's a yak on the stack to fix.
There's still a lot to be desired in terms of functionality and
usability, but this is a start. When using the clone tool, you
can press Alt to sample a location, and then the brush will clone
the color from there.
