po/colorpicker edit - edit area & point

[TurboGit]

Allow for editing area & point as hinted by the tooltip.

@jenshannoschwalm : This is based on top of your PR but it independent, can you test?

How it works:

1. click on picker icon
2. right click on a sample
3. move it / change size of area
4. deselect the picker

I'd like to avoid 1 and as soon as we right click we enter in edit mode and maybe right-click again to update the sample. Seems a better user interaction to me, what do you think?