Daisy chain date $emit

Solves a use case where I have the datepicker inside another directive which may or may not have a second date requirement... similar to a date-range implementation, but using two single-point pickers that can talk upwards. The `$emit` in the screen shot is the final `$emit` coming from another directive.
![datepicker-daisychain-emit](https://cloud.githubusercontent.com/assets/1619521/2746603/a10540ee-c74b-11e3-856c-ce3d438a436c.png)