[clarity/consistency] rename /explorev2/ -> /explore/ (#2802)

* rename /explorev2/ -> /explore/

* add redirect for existing explorev2 urls

* fix long line

* remove extra line

* fix missed ref in spec

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

@@ -0,0 +1,39 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { FormGroup, FormControl } from 'react-bootstrap';
+
+const propTypes = {
+  name: PropTypes.string.isRequired,
+  label: PropTypes.string,
+  description: PropTypes.string,
+  onChange: PropTypes.func,
+  value: PropTypes.string,
+};
+
+const defaultProps = {
+  label: null,
+  description: null,
+  onChange: () => {},
+  value: '',
+};
+
+export default class TextAreaControl extends React.Component {
+  onChange(event) {
+    this.props.onChange(event.target.value);
+  }
+  render() {
+    return (
+      <FormGroup controlId="formControlsTextarea">
+        <FormControl
+          componentClass="textarea"
+          placeholder="textarea"
+          onChange={this.onChange.bind(this)}
+          value={this.props.value}
+        />
+      </FormGroup>
+    );
+  }
+}
+
+TextAreaControl.propTypes = propTypes;
+TextAreaControl.defaultProps = defaultProps;