fix(rxModalAction): fix #594, modal actions to be buttons, not links

![rxmodalaction-1](https://cloud.githubusercontent.com/assets/33945/4799053/326bcec2-5e19-11e4-889b-1640c40bf104.png)
![rxmodalaction-2](https://cloud.githubusercontent.com/assets/33945/4799054/328a8d1c-5e19-11e4-9bc1-91ca748e069f.png)

Hi @parlarjb - the `classes` directives bring in the actual class names into the `rxModalAction` template:

https://github.com/rackerlabs/encore-ui/blob/594-rxModalForm-buttons/src/rxModalAction/templates/rxModalAction.html#L2