add ColorPicker and NumPad widgets from chaosbuffalolabs (thanks!)
fix usage of numpad for colopicker
simplify Numpad and document its propperties, adapt colorpicker
Merge branch 'master' of github.com:kivy/kivy into color_picker
Merge branch 'master' into color_picker
fix various issues with color_picker
Merge branch 'master' into color_picker
change color of colorwheel to ReferenceListProperty of BoundedNumericProperties
remove NumPad and use sliders instead in ColorPicker
Merge pull request #833 from kivy/color_picker

add ColorPicker and NumPad widgets from chaosbuffalolabs (thanks!)