Remove use of deprecated React.PropTypes

Replace all uses of React.PropTypes with PropTypes and importing PropTypes from
'prop-types'.

src/components/views/messages/TextualBody.js

@@ -18,6 +18,7 @@ limitations under the License.
 
 import React from 'react';
 import ReactDOM from 'react-dom';
+import PropTypes from 'prop-types';
 import highlight from 'highlight.js';
 import * as HtmlUtils from '../../../HtmlUtils';
 import * as linkify from 'linkifyjs';
@@ -43,19 +44,19 @@ module.exports = React.createClass({
 
     propTypes: {
         /* the MatrixEvent to show */
-        mxEvent: React.PropTypes.object.isRequired,
+        mxEvent: PropTypes.object.isRequired,
 
         /* a list of words to highlight */
-        highlights: React.PropTypes.array,
+        highlights: PropTypes.array,
 
         /* link URL for the highlights */
-        highlightLink: React.PropTypes.string,
+        highlightLink: PropTypes.string,
 
         /* should show URL previews for this event */
-        showUrlPreview: React.PropTypes.bool,
+        showUrlPreview: PropTypes.bool,
 
         /* callback for when our widget has loaded */
-        onWidgetLoad: React.PropTypes.func,
+        onWidgetLoad: PropTypes.func,
     },
 
     getInitialState: function() {