Set boolean value to HTMLInputElement.checked

See http://www.whatwg.org/specs/web-apps/current-work/multipage/the-input-element.html#attr-input-checked
Merge pull request #1266 from fredj/input_checked

Set boolean value to HTMLInputElement.checked
Getter and setter support for bindTo
Add tests for ol.Object#bindTo getters and setters
Remove 'valueAsNumber' property from ol.dom.Input

Use bindTo.transform functions instead
Notify target object after transform functions change