Now inside the <template> of a SkyElement you can use
on-eventName="method" on any element to add event listeners.

For example you can write <sky-button on-click="handleClick">
and then define handleClick(event) on the element class that
contains the button.

In adding this and tests I also realized that property bindings
were not setup on the initial call to bind(), which is now
fixed in this patch (See change to Node.prototype.bind).

R=eseidel@google.com, rafaelw@chromium.org

Review URL: https://codereview.chromium.org/812713005