Remove use of deprecated React.PropTypes

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

src/components/views/dialogs/BaseDialog.js

@@ -15,6 +15,7 @@ limitations under the License.
 */
 
 import React from 'react';
+import PropTypes from 'prop-types';
 
 import { KeyCode } from '../../../Keyboard';
 import AccessibleButton from '../elements/AccessibleButton';
@@ -31,20 +32,20 @@ export default React.createClass({
 
     propTypes: {
         // onFinished callback to call when Escape is pressed
-        onFinished: React.PropTypes.func.isRequired,
+        onFinished: PropTypes.func.isRequired,
 
         // callback to call when Enter is pressed
-        onEnterPressed: React.PropTypes.func,
+        onEnterPressed: PropTypes.func,
 
         // CSS class to apply to dialog div
-        className: React.PropTypes.string,
+        className: PropTypes.string,
 
         // Title for the dialog.
         // (could probably actually be something more complicated than a string if desired)
-        title: React.PropTypes.string.isRequired,
+        title: PropTypes.string.isRequired,
 
         // children should be the content of the dialog
-        children: React.PropTypes.node,
+        children: PropTypes.node,
     },
 
     _onKeyDown: function(e) {