Rename helper as it is only a helper for the datepicker modal and no generic helper

frontend/src/app/components/datepicker/datepicker.modal.helper.ts

@@ -32,7 +32,7 @@ import {DatePicker} from "core-app/modules/common/op-date-picker/datepicker";
 import {DateOption} from "flatpickr/dist/types/options";
 
 @Injectable({ providedIn: 'root' })
-export class DatepickerHelper {
+export class DatePickerModalHelper {
   public currentlyActivatedDateField:DateKeys;
 
   /**

frontend/src/app/components/datepicker/datepicker.modal.ts

@@ -46,7 +46,7 @@ import {TimezoneService} from "core-components/datetime/timezone.service";
 import {DatePicker} from "core-app/modules/common/op-date-picker/datepicker";
 import {HalResourceEditingService} from "core-app/modules/fields/edit/services/hal-resource-editing.service";
 import {ResourceChangeset} from "core-app/modules/fields/changeset/resource-changeset";
-import {DatepickerHelper} from "core-components/datepicker/datepicker.helper";
+import {DatePickerModalHelper} from "core-components/datepicker/datepicker.modal.helper";
 
 export type DateKeys = 'date'|'start'|'end';
 
@@ -60,7 +60,7 @@ export class DatePickerModal extends OpModalComponent implements AfterViewInit {
   @InjectField() I18n:I18nService;
   @InjectField() timezoneService:TimezoneService;
   @InjectField() halEditing:HalResourceEditingService;
-  @InjectField() datepickerHelper:DatepickerHelper;
+  @InjectField() datepickerHelper:DatePickerModalHelper;
 
   text = {
     save: this.I18n.t('js.button_save'),