Remove use of deprecated React.PropTypes

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

src/components/views/create_room/CreateRoomButton.js

@@ -17,11 +17,12 @@ limitations under the License.
 'use strict';
 
 import React from 'react';
+import PropTypes from 'prop-types';
 import { _t } from '../../../languageHandler';
 module.exports = React.createClass({
     displayName: 'CreateRoomButton',
     propTypes: {
-        onCreateRoom: React.PropTypes.func,
+        onCreateRoom: PropTypes.func,
     },
 
     getDefaultProps: function() {

src/components/views/create_room/Presets.js

@@ -17,6 +17,7 @@ limitations under the License.
 'use strict';
 
 const React = require('react');
+import PropTypes from 'prop-types';
 import { _t } from '../../../languageHandler';
 
 const Presets = {
@@ -28,8 +29,8 @@ const Presets = {
 module.exports = React.createClass({
     displayName: 'CreateRoomPresets',
     propTypes: {
-        onChange: React.PropTypes.func,
-        preset: React.PropTypes.string,
+        onChange: PropTypes.func,
+        preset: PropTypes.string,
     },
 
     Presets: Presets,

src/components/views/create_room/RoomAlias.js

@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 const React = require('react');
+import PropTypes from 'prop-types';
 import { _t } from '../../../languageHandler';
 
 module.exports = React.createClass({
@@ -22,9 +23,9 @@ module.exports = React.createClass({
     propTypes: {
         // Specifying a homeserver will make magical things happen when you,
         // e.g. start typing in the room alias box.
-        homeserver: React.PropTypes.string,
-        alias: React.PropTypes.string,
-        onChange: React.PropTypes.func,
+        homeserver: PropTypes.string,
+        alias: PropTypes.string,
+        onChange: PropTypes.func,
     },
 
     getDefaultProps: function() {