add dark theme to calendar date picker.

Tried to use the same colors as the RadialTimePicker dark theme. 
![image](https://cloud.githubusercontent.com/assets/564247/2725902/a57f1cac-c5b2-11e3-8744-9e34bebc4f88.png)

![image](https://cloud.githubusercontent.com/assets/564247/2725903/b1ae9566-c5b2-11e3-86b3-f81715d68e73.png)


The light still looks the same: 
![image](https://cloud.githubusercontent.com/assets/564247/2725860/d2bcd994-c5b1-11e3-8698-79cd5c72d770.png)

![image](https://cloud.githubusercontent.com/assets/564247/2725875/ef340174-c5b1-11e3-872a-22bfcbcdce21.png)