title: Adding hard coded row in element ui table
body: <p>I have a table using element-ui table. 
  I need to create a first hard coded row, with some text and a button.
  It should not follow the normal table cells. just a row to take the full width of the table.
  I cant find a way to do it - it dose not need a column - label or anything. just the same table with a first hard coded row. couldnt find a way to do it. would appreciate any help.</p>
  
  <p>The table looks something like this: </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;template&gt;
    &lt;section class="order-list"&gt;
      &lt;el-table style="width: 100%" :data="orders" v-if="orders"&gt;
        &lt;el-table-column class-name="list-title" min-width="140" prop="title" label="Title"&gt;&lt;/el-table-column&gt;
        &lt;el-table-column class-name="list-edit-btn" min-width="100" label&gt;&lt;/el-table-column&gt;
        &lt;el-table-column min-width="100" prop="dpCount" label="# of DP"&gt;
          &lt;template slot-scope="scope"&gt;
            &lt;p&gt;{{ scope.row.dpCount.toLocaleString() }}&lt;/p&gt;
          &lt;/template&gt;
        &lt;/el-table-column&gt;
        &lt;el-table-column
          class-name="description"
          prop="description"
          min-width="160"
          label="Description"
        &gt;&lt;/el-table-column&gt;
        &lt;el-table-column min-width="270" prop="createdAt" label="Generation Status"&gt;
          &lt;template slot-scope="scope"&gt;
            &lt;order-status :order="scope.row" /&gt;
          &lt;/template&gt;
        &lt;/el-table-column&gt;
        &lt;el-table-column class-name="list-actions" min-width="240" label&gt;
          &lt;template slot-scope="scope"&gt;
            &lt;el-button
              size="mini"
              class="sample-btn"
              @click="goToLink(scope.row.sample.url)"
              :disabled="!scope.row.sample.url"
              round
            &gt;Sample&lt;/el-button&gt;
            &lt;el-button
              class="btn"
              @click="goToLink(scope.row.downloadUrl)"
              :disabled="!scope.row.downloadUrl"
              size="mini"
              type="primary"
              round
            &gt;Full Download&lt;/el-button&gt;
          &lt;/template&gt;
        &lt;/el-table-column&gt;
      &lt;/el-table&gt;
    &lt;/section&gt;
  &lt;/template&gt;</code></pre>
  </div>
  </div>
  </p>