Improve date picker controls.

![screen shot 2014-09-03 at 10 59 20 pm](https://cloud.githubusercontent.com/assets/669/4144747/dfb604c8-33e7-11e4-99e4-e003ed09e6bf.png)

* added placeholder text for accepted date format
* if user clicks in text field, date picker does not pop up
* only if user clicks calendar button does date picker show
* fixed issue with some date formats not being honored by the date picker
* fixed issue where clicking the month/year would not zoom out to select year

![screen shot 2014-09-03 at 11 00 41 pm](https://cloud.githubusercontent.com/assets/669/4144754/118d46c8-33e8-11e4-8a28-3a2359459cd0.png)