style(rxForm): styles/class to allow full-width; Fix #413

Added `full-width` common class and updated rxFormOptionTable styles to allow for its use. Also, some minor cleanup.

![image](https://cloud.githubusercontent.com/assets/706039/3728738/73897866-16af-11e4-82c6-585aa719cd0c.png)

![image](https://cloud.githubusercontent.com/assets/706039/3728739/78254206-16af-11e4-945d-0e551d1be4ba.png)