Action buttons

Added support for action buttons which are displayed in the right of the top bar.

![ios simulator screen shot jul 30 2014 2 43 12 pm](https://cloud.githubusercontent.com/assets/2208284/3754331/0960593e-181a-11e4-9ce3-26986c0a6f80.png)


![ios simulator screen shot jul 30 2014 2 43 32 pm](https://cloud.githubusercontent.com/assets/2208284/3754306/b88e8594-1819-11e4-97bd-12db42930e2c.png)

NSString *const (remove space after *)