datepicker start date and end date don't work for dynamic values (max, min)

[yonida]

1. set two datepicker component, first bound to startDate, second bound to endDate.
2. set on the first component max value to endDate, and on the seconds component min value to startDate
3. pick a startDate, then endDate value can be set to a date before the startDate.
4. startDate can be set to be after endDate

** I think it works with static values.

[yonida]

This can be fixed by observing min and max values, and then calling picker.set('min', this.get('min')) or picker.set('max', this.get('max')). very simple fix.