fix(forms): labels should not shift unless values change

Fixes #1008.

@vladikoff or @shane-tomlinson r?
Can this be made part of `togglePlaceholderPattern`?  Not for this PR, but it would be nice to simplify attaching behaviors like this through a declaration on the class:

```js
var Module = BaseView.extend({
  behaviors: [ FloatingPlaceholders ]
...
});
```