[explore] include ControlHeader as part of Control interface (#2809)

* [explore] include ControlHeader as part of Control interface

* Adressing comments

superset/assets/javascripts/explore/components/controls/TextAreaControl.jsx

@@ -1,6 +1,7 @@
 import React from 'react';
 import PropTypes from 'prop-types';
 import { FormGroup, FormControl } from 'react-bootstrap';
+import ControlHeader from '../ControlHeader';
 
 const propTypes = {
   name: PropTypes.string.isRequired,
@@ -23,14 +24,17 @@ export default class TextAreaControl extends React.Component {
   }
   render() {
     return (
-      <FormGroup controlId="formControlsTextarea">
-        <FormControl
-          componentClass="textarea"
-          placeholder="textarea"
-          onChange={this.onChange.bind(this)}
-          value={this.props.value}
-        />
-      </FormGroup>
+      <div>
+        <ControlHeader {...this.props} />
+        <FormGroup controlId="formControlsTextarea">
+          <FormControl
+            componentClass="textarea"
+            placeholder="textarea"
+            onChange={this.onChange.bind(this)}
+            value={this.props.value}
+          />
+        </FormGroup>
+      </div>
     );
   }
 }