Change mandatory to isRequired

lib/Db/Question.php

src/components/Questions/Question.vue

src/components/Questions/QuestionDate.vue

src/components/Questions/QuestionDropdown.vue

src/components/Questions/QuestionLong.vue

src/components/Questions/QuestionMultiple.vue

src/components/Questions/QuestionShort.vue

src/mixins/QuestionMixin.js

src/views/Create.vue

src/views/Submit.vue