Replace React.PropTypes with usage of the prop-types package

Signed-off-by: Michael Telatynski <7t3chguy@gmail.com>

src/components/views/elements/Dropdown.js

@@ -1,5 +1,6 @@
 /*
 Copyright 2017 Vector Creations Ltd
+Copyright 2019 Michael Telatynski <7t3chguy@gmail.com>
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -58,7 +59,7 @@ class MenuOption extends React.Component {
 
 MenuOption.propTypes = {
     children: PropTypes.oneOfType([
-      PropTypes.arrayOf(React.PropTypes.node),
+      PropTypes.arrayOf(PropTypes.node),
       PropTypes.node,
     ]),
     highlighted: PropTypes.bool,

src/components/views/elements/ImageView.js

@@ -17,7 +17,8 @@ limitations under the License.
 
 'use strict';
 
-const React = require('react');
+import React from 'react';
+import PropTypes from 'prop-types';
 
 const MatrixClientPeg = require('../../../MatrixClientPeg');
 
@@ -30,19 +31,19 @@ import { _t } from '../../../languageHandler';
 
 export default class ImageView extends React.Component {
     static propTypes = {
-        src: React.PropTypes.string.isRequired, // the source of the image being displayed
-        name: React.PropTypes.string, // the main title ('name') for the image
-        link: React.PropTypes.string, // the link (if any) applied to the name of the image
-        width: React.PropTypes.number, // width of the image src in pixels
-        height: React.PropTypes.number, // height of the image src in pixels
-        fileSize: React.PropTypes.number, // size of the image src in bytes
-        onFinished: React.PropTypes.func.isRequired, // callback when the lightbox is dismissed
+        src: PropTypes.string.isRequired, // the source of the image being displayed
+        name: PropTypes.string, // the main title ('name') for the image
+        link: PropTypes.string, // the link (if any) applied to the name of the image
+        width: PropTypes.number, // width of the image src in pixels
+        height: PropTypes.number, // height of the image src in pixels
+        fileSize: PropTypes.number, // size of the image src in bytes
+        onFinished: PropTypes.func.isRequired, // callback when the lightbox is dismissed
 
         // the event (if any) that the Image is displaying. Used for event-specific stuff like
         // redactions, senders, timestamps etc.  Other descriptors are taken from the explicit
         // properties above, which let us use lightboxes to display images which aren't associated
         // with events.
-        mxEvent: React.PropTypes.object,
+        mxEvent: PropTypes.object,
     };
 
     constructor(props) {

src/components/views/elements/Tooltip.js

@@ -1,6 +1,7 @@
 /*
 Copyright 2015, 2016 OpenMarket Ltd
 Copyright 2019 New Vector Ltd
+Copyright 2019 Michael Telatynski <7t3chguy@gmail.com>
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -18,6 +19,7 @@ limitations under the License.
 
 import React from 'react';
 import ReactDOM from 'react-dom';
+import PropTypes from 'prop-types';
 import dis from '../../../dispatcher';
 import classNames from 'classnames';
 
@@ -28,15 +30,15 @@ module.exports = React.createClass({
 
     propTypes: {
         // Class applied to the element used to position the tooltip
-        className: React.PropTypes.string,
+        className: PropTypes.string,
         // Class applied to the tooltip itself
-        tooltipClassName: React.PropTypes.string,
+        tooltipClassName: PropTypes.string,
         // Whether the tooltip is visible or hidden.
         // The hidden state allows animating the tooltip away via CSS.
         // Defaults to visible if unset.
-        visible: React.PropTypes.bool,
+        visible: PropTypes.bool,
         // the react element to put into the tooltip
-        label: React.PropTypes.node,
+        label: PropTypes.node,
     },
 
     getDefaultProps() {

src/components/views/elements/UserSelector.js

@@ -25,7 +25,7 @@ module.exports = React.createClass({
 
     propTypes: {
         onChange: PropTypes.func,
-        selected_users: PropTypes.arrayOf(React.PropTypes.string),
+        selected_users: PropTypes.arrayOf(PropTypes.string),
     },
 
     getDefaultProps: function() {