fix several issues with the color controller:
fix several issues with the color controller:

- fix the color picker dimensions to allow for the alpha channel slider in there
- fix the mouse & touch position calculations, reckoning with the dat.gui container or other parent possibly having a 'position:fixed' style to make it stick to the edge of the viewport: when the page is scrolled the color picker would not produce the correct picker/color coordinates anymore.

GerHobbelt/dat.gui,GerHobbelt/dat.gui