Fix upload cancel in e2e rooms

This is a bit of a mess of passing promises around - we weren't
taking the right promise to pass to cancelUpload.

Also e2e uploads take time to read into memory & encrypt, so allow
cancelling them during those phases too, even though we can't abort
those phases before they're done - we do mark the upload as cancelled
though so filter the current uploads for cancelled ones.

Fixes https://github.com/vector-im/riot-web/issues/4891

src/components/structures/RoomView.js

@@ -543,6 +543,7 @@ module.exports = React.createClass({
             case 'notifier_enabled':
             case 'upload_started':
             case 'upload_finished':
+            case 'upload_canceled':
                 this.forceUpdate();
                 break;
             case 'call_state':

src/components/structures/UploadBar.js

@@ -16,7 +16,7 @@ limitations under the License.
 
 const React = require('react');
 import PropTypes from 'prop-types';
-const ContentMessages = require('../../ContentMessages');
+import ContentMessages from '../../ContentMessages';
 const dis = require('../../dispatcher');
 const filesize = require('filesize');
 import { _t } from '../../languageHandler';
@@ -40,6 +40,7 @@ module.exports = React.createClass({displayName: 'UploadBar',
         switch (payload.action) {
             case 'upload_progress':
             case 'upload_finished':
+            case 'upload_canceled':
             case 'upload_failed':
                 if (this.mounted) this.forceUpdate();
                 break;