message: Added reset button
diff: <div class="opt-container">
  <h1 class="page-header">{{ i18n('opt_title') }}
  <a class="new-version" v-if="isNewVersion" href="http://www.crimx.com/crx-saladict/" target="_blank">{{ i18n('opt_new_version') }}</a>
  + <button type="button" class="btn btn-default btn-reset" @click="handleReset">{{ i18n('opt_reset') }}</button>
  </h1>
  <div class="opt-item">
  @@ -287,6 +288,9 @@ export default {
  this.dicts[id].height = 0
  })
  },
  + handleReset () {
  + storage.sync.set({config: defaultConfig})
  + },
  handlePanelHeadClick (id, i) {
  let height = this.dicts[id].height > 0 ? 0 : this.$refs.dict[i].firstChild.offsetHeight
  this.clearDictsHeight()
  @@ -518,6 +522,16 @@ kbd {
  color: #16a085;
  }
  +.page-header {
  + position: relative;
  +}
  +
  +.btn-reset {
  + position: absolute;
  + bottom: 8px;
  + right: 0;
  +}
  +
  .opt-item {
  @extend .row;
  position: relative;
  