message: Implement started page for vue platform:
diff: <template>
  <div :class="css.root">
  <div v-if="hasTitle" :class="css.header"><h3><survey-string :locString="survey.locTitle"/></h3></div>
  + <template v-if="survey.state === 'starting'">
  + <div :class="css.body">
  + <survey-page :id="survey.startedPage.id" :survey="survey" :page="survey.startedPage" :css="css" />
  + </div>
  + <div v-if="survey.isNavigationButtonsShowing" :class="css.footer">
  + <input type="button" :value="survey.startSurveyText" :class="getNavBtnClasses('start')" @click="start"/>
  + </div>
  + </template>
  <template v-if="survey.state === 'running'">
  <div :class="css.body">
  <survey-progress v-if="survey.showProgressBar =='top'" :survey="survey" :css="css"/>
  