fix(date picker): minDate is now exclusive

This PR makes minDate behaviour match maxDate, and allows the date provided in the option to be
selected.

BREAKING CHANGE: The date provided to the component via the minDate option is now selectable by
users. If you are using the mindate functionality, you will need to adjust the dates you pass into
the component to ensure the correct dates are included/excluded.

fix #923

src/moj/components/date-picker/date-picker.js

@@ -435,7 +435,7 @@ Datepicker.prototype.setWeekStartDay = function () {
  *
  */
 Datepicker.prototype.isExcludedDate = function (date) {
-  if (this.minDate && this.minDate > date) {
+  if (this.minDate && this.minDate >= date) {
     return true;
   }