feat(datepicker): allow suppression of log error

- Add `$datepickerSuppressError` injectable to allow suppressing of error message

Closes #3836
Closes #4115

Author: Blackbaud-PatrickOFriel

Diff for: src/datepicker/datepicker.js

@@ -1,5 +1,7 @@
 angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootstrap.position'])
 
+.value('$datepickerSuppressError', false)
+
 .constant('datepickerConfig', {
   formatDay: 'dd',
   formatMonth: 'MMMM',
@@ -18,7 +20,7 @@ angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootst
   shortcutPropagation: false
 })
 
-.controller('DatepickerController', ['$scope', '$attrs', '$parse', '$interpolate', '$log', 'dateFilter', 'datepickerConfig', function($scope, $attrs, $parse, $interpolate, $log, dateFilter, datepickerConfig) {
+.controller('DatepickerController', ['$scope', '$attrs', '$parse', '$interpolate', '$log', 'dateFilter', 'datepickerConfig', '$datepickerSuppressError', function($scope, $attrs, $parse, $interpolate, $log, dateFilter, datepickerConfig, $datepickerSuppressError) {
   var self = this,
       ngModelCtrl = { $setViewValue: angular.noop }; // nullModelCtrl;
 
@@ -82,7 +84,7 @@ angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootst
 
       if ( isValid ) {
         this.activeDate = date;
-      } else {
+      } else if ( !$datepickerSuppressError ) {
         $log.error('Datepicker directive: "ng-model" value must be a Date object, a number of milliseconds since 01.01.1970 or a string representing an RFC2822 or ISO 8601 date.');
       }
     }