Fix null end_date toggling on patient builder's data criteria

#### Story ####
- https://www.pivotaltracker.com/story/show/64921386

#### Notes ####
- on toggling <code>end_date</code> via undefined checkbox, if unchecked then set the datepicker's date to the current day (requires <code>$().datepicker('update')</code>) and the timepicker's time to 8:00AM

#### Screenshots ####
- set date and time to arbitrary values
  - ![screen shot 2014-02-20 at 1 28 33 pm](https://f.cloud.github.com/assets/456952/2221786/3ca43c60-9a5d-11e3-8e22-77a4938830ff.png)
- apply UNDEFINED to end date
  - ![screen shot 2014-02-20 at 1 28 39 pm](https://f.cloud.github.com/assets/456952/2221784/3ca1d4a2-9a5d-11e3-9236-3dda4aa67137.png)
- unapply UNDEFINED on end date
  - ![screen shot 2014-02-20 at 1 28 43 pm](https://f.cloud.github.com/assets/456952/2221785/3ca20c2e-9a5d-11e3-990e-f3b0cfdcddf3.png)