[#1993] Datepicker - disable year/month navigation if min date specified 

I am trying to determine in _refreshView for all 3 (day/month/year) pickers if some navigation should be disabled.
After I set the result in the scope I am using the result in the templates like this: ng-disabled="navPrevDisabled" .

I am just disabling the buttons for now but if the approach is correct I can prevent it from keyboard as well hooking into 'move()' .