Implemented `setReadOnly` method.
Implemented `setReadOnly` method.

Calling `setReadOnly` with `true` parameter will make the canvas not editable. To return the canvas the drawing state `setReadOnly` should be called again with `false` parameter.

trsanders/responsive-sketchpad,trsanders/responsive-sketchpad,theisensanders-wf/responsive-sketchpad,theisensanders-wf/responsive-sketchpad