Add of posibility to select end date before start date, and vice-versa.

Add of highlighing of changed field.

app/assets/stylesheets/content/_in_place_editing.sass

@@ -29,6 +29,7 @@
 $inplace-edit--border-color: #ddd
 $inplace-edit--dark-background: #f8f8f8
 $inplace-edit--color--very-dark: #cacaca
+$inplace-edit--color-highlight: #0a97dd
 $inplace-edit--selected-date-border-color: #008bd0
 $inplace-edit--color-highlight: #0a97dd
 

frontend/app/ui_components/index.js

@@ -46,6 +46,9 @@ angular.module('openproject.uiComponents')
   .directive('opTime', ['TimezoneService', require('./date/time-directive')])
   .directive('opDateTime', ['$compile', 'TimezoneService', require('./date/date-time-directive')])
   .directive('emptyElement', [require('./empty-element-directive')])
+  .directive('opDateRangePicker', ['TimezoneService', 'ConfigurationService', 
+             'I18n', '$timeout', 'WorkPackageFieldService',
+             'EditableFieldsState', 'Datepicker', require('./date/date-range-picker-directive')])
   .constant('ENTER_KEY', 13)
   .directive('executeOnEnter', ['ENTER_KEY', require(
     './execute-on-enter-directive')])

frontend/app/work_packages/models/index.js

@@ -28,5 +28,4 @@
 
 angular.module('openproject.workPackages.models')
   .factory('WorkPackageAuthorization', require('./work-package-authorization'))
-  .factory('Datepicker', ['TimezoneService', 'ConfigurationService', 
-                          '$timeout', require('./datepicker.js')]);
+  .factory('Datepicker', ['TimezoneService', 'ConfigurationService', '$timeout', require('./datepicker.js')])