ability to pass in a maxWidthClass class name binding

I'd like the ability to have the input look different when it reaches max width. Maybe something like:

```
{{input autoresize=true maxWidthClass="lol cats" max-width=300}}

## initial rendering

## when the width hits 300px

```

If this sounds OK to you, I'll make a PR. @tim-evans

also, perhaps an action that can be fired when we reach max width. I feel more iffy about this though.

No file or test is named. Start by locating the Ember input's existing autoresize and max-width handling, then compare it with the requested maxWidthClass example. Done means the class binding appears when the input reaches the configured maximum width, with the optional action considered separately.

Escrito por el modelo de indexación a partir del texto del issue.