message: added needed import for ts
diff: import {Component, Prop} from 'vue-property-decorator'
  import {default as Question} from './question'
  import {QuestionMatrixDropdownModel} from '../question_matrixdropdown'
  + import {MatrixDropdownRowModelBase} from '../question_matrixdropdownbase'
  @Component
  export default class MatrixDropdown extends Question<QuestionMatrixDropdownModel> {
  