Auto-fill fieldset and property aliases in Config

![autopopulate-sm](https://f.cloud.github.com/assets/1396376/2306087/33d0ee16-a279-11e3-906e-13e9bc663677.gif)

Fixes #32 

* Add new aliasIsDirty property, init for existing data
* Bind label control's keyup to populate the `alias` property (when it's not dirty) using Umbraco's helpers
* Mark alias dirty on keyup