Rough style for new upload bar

This repurposes ProgressBar which was not used anywhere in code.

res/css/structures/_UploadBar.scss

@@ -1,5 +1,5 @@
 /*
-Copyright 2015, 2016 OpenMarket Ltd
+Copyright 2015, 2016, 2021 The Matrix.org Foundation C.I.C.
 
 Licensed under the Apache License, Version 2.0 (the "License");
 you may not use this file except in compliance with the License.
@@ -15,24 +15,15 @@ limitations under the License.
 */
 
 .mx_UploadBar {
-    position: relative;
-}
+    padding-left: 65px; // line up with the shield area in the composer
 
-.mx_UploadBar_uploadProgressOuter {
-    height: 5px;
-    margin-left: 63px;
-    margin-top: -1px;
-    padding-bottom: 5px;
-}
-
-.mx_UploadBar_uploadProgressInner {
-    background-color: $accent-color;
-    height: 5px;
+    .mx_ProgressBar {
+        width: calc(100% - 40px); // cheating at a right margin
+    }
 }
 
 .mx_UploadBar_uploadFilename {
     margin-top: 5px;
-    margin-left: 65px;
     opacity: 0.5;
     color: $primary-fg-color;
 }
@@ -52,10 +43,3 @@ limitations under the License.
     cursor: pointer;
     z-index: 1;
 }
-
-.mx_UploadBar_uploadBytes {
-    float: right;
-    margin-top: 5px;
-    margin-right: 30px;
-    color: $accent-color;
-}