uix: `disabled` property for base widgets
uix: first pass at making some compound widgets honor `disabled`
property.
uix:Widgets make sure all compound widgets work with disabled
increase size of atlas to 1024 for accomodating all images in one atlas
uix: Widget move disabling of child widgets to `on_disabled` instead of
binding. and move back to a 512 image for atlas.
uix: Widget.disabled final pass making sure every widget honors disabled
property and doc fixes.
uix:widgets.disabled fix kv for slider
Merge pull request #1209 from kivy/widgets.disabled

Widgets.disabled