Use .prop instead of .attr when we deal with properties

In core we still have line like

$("input").attr("disabled", ''); //bad

A least it should be

$("input").attr("disabled", false);

But .prop is made for properties, we should use it. http://api.jquery.com/prop/.

# Careful when you want to set to false.
To set a native property to false use

$("input").prop("disabled", false);

You can not add the property again if you use removeProp on native properties.

$("input").removeProp("disabled", false);