Added option to include month/year select lists on calendars

The select lists are enabled using the options { showDropdowns: true }. They should obey the min/max dates as well as the currently selected dates. I have also added a simple example of use.

![cal](https://f.cloud.github.com/assets/239450/208122/c1150b72-8213-11e2-8251-97cdc47af03d.png)