document_view fields as auto-sizing textareas

This addresses [issue 12](https://github.com/gterrono/meteor-admin-ui/issues/12), which is pretty important for long-form prose being stored in the db.

This changes the document_view input.field elements to be textarea.field elements instead of inputs and uses Jack Moore’s [autosize library](http://www.jacklmoore.com/autosize) to make them auto-size to fit the proper height.

Some additional things:

*   I made the textareas 100% width (with the help of border-box)
*   the 2nd commit fixes a little quirk that happens with resizing and the reactivity of the page during a save

Let me know if there’s anything different that should be done with the pull request.