refactor(DateObject): Remove for loop in favor of .filter() and .forEach()

Constructor now iteraates over first argument keys, filters out invalid keys, and sets properties on

the DateObject. Previous implemntation requried adding ignore comments for uncovered code. The new

code has few branches and cannot inherite properties from the constructor objects parent(s)

Author: dalelotts

src/js/datetimepicker.js

@@ -415,14 +415,13 @@
 
       var validProperties = ['utcDateValue', 'localDateValue', 'display', 'active', 'selectable', 'past', 'future']
 
-      for (var prop in arguments[0]) {
-        /* istanbul ignore else */
-        // noinspection JSUnfilteredForInLoop
-        if (validProperties.indexOf(prop) >= 0) {
-          // noinspection JSUnfilteredForInLoop
-          this[prop] = arguments[0][prop]
-        }
-      }
+      var constructorObject = arguments[0]
+
+      Object.keys(constructorObject).filter(function (key) {
+        return validProperties.indexOf(key) >= 0
+      }).forEach(function (key) {
+        this[key] = constructorObject[key]
+      }, this)
     }
 
     return directiveDefinition