[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/URLShortLinkButton.jsx

@@ -0,0 +1,63 @@
+import React from 'react';
+import PropTypes from 'prop-types';
+import { Popover, OverlayTrigger } from 'react-bootstrap';
+import CopyToClipboard from './../../components/CopyToClipboard';
+import { getShortUrl } from '../../../utils/common';
+
+const propTypes = {
+  slice: PropTypes.object.isRequired,
+};
+
+export default class URLShortLinkButton extends React.Component {
+  constructor(props) {
+    super(props);
+    this.state = {
+      shortUrl: '',
+    };
+  }
+
+  onShortUrlSuccess(data) {
+    this.setState({
+      shortUrl: data,
+    });
+  }
+
+  getCopyUrl() {
+    const longUrl = window.location.pathname + window.location.search;
+    getShortUrl(longUrl, this.onShortUrlSuccess.bind(this));
+  }
+
+  renderPopover() {
+    const emailBody = `Check out this slice: ${this.state.shortUrl}`;
+    return (
+      <Popover id="shorturl-popover">
+        <CopyToClipboard
+          text={this.state.shortUrl}
+          copyNode={<i className="fa fa-clipboard" title="Copy to clipboard" />}
+        />
+        &nbsp;&nbsp;
+        <a href={`mailto:?Subject=Superset%20Slice%20&Body=${emailBody}`}>
+          <i className="fa fa-envelope" />
+        </a>
+      </Popover>
+    );
+  }
+
+  render() {
+    return (
+      <OverlayTrigger
+        trigger="click"
+        rootClose
+        placement="left"
+        onEnter={this.getCopyUrl.bind(this)}
+        overlay={this.renderPopover()}
+      >
+        <span className="btn btn-default btn-sm">
+          <i className="fa fa-link" />&nbsp;
+        </span>
+      </OverlayTrigger>
+    );
+  }
+}
+
+URLShortLinkButton.propTypes = propTypes;