Adding a way to override Input Addon wrapper

I was trying to make a "spinner" (up and down button) addon on an input and was having some issues because of the default wrapper class which is "input-group-addon".

This does not change the default behavior as "wrapAddon(Before|After)" defaults to true, but lets the user to override it if he wants to provide it's own wrapper.

One thing though, I wasn't sure about calling it "wrapAddon..." and add a "getDefaultProps" function OR find a better name that says the inverse so you don't need the getDefaultProps. I ended up doing the former because it looked more intuitive to me.

With this, it enables you to have so slick addons like 

    function upClick () {}
    function downClick () {}
    var addon = (
      <div className="input-group-spinner">
        <Button><Glyphicon glyph="chevron-up" onClick={upClick} /></Button>
        <Button><Glyphicon glyph="chevron-down" onClick={downClick} /></Button>
      </div>
    );
    <Input type="text" addonAfter={addon} wrapAddonAfter={false}  />

Let me know what you think about that