Update demo page
Update demo page

* Using three columns instead of two, to allow seeing updates to open
pickers with max/min date restrictions after the min/max dates change.
* Reorganized a bit
* Added second callback picker which is open, and a reset button.

DanTalash/angular-datepicker,g00fy-/angular-datepicker,pankas87/angular-datepicker-dirty-fix,frontapp/angular-datepicker,DanTalash/angular-datepicker,g00fy-/angular-datepicker,pankas87/angular-datepicker-dirty-fix,frontapp/angular-datepicker