Fix icon and css for button to switch between video and chat on mobile layout

After upgrade to fontawesome 5, fa-exchange is now fa-exchange-alt
Fix also css after changes on icons.

static/sfu.css

@@ -1150,7 +1150,7 @@ header .collapse {
 
     .collapse-video {
         left: inherit;
-        right: 60px;
+        right: 10px;
     }
 
     .close-chat {

static/sfu.html

@@ -98,7 +98,7 @@
             </div>
             <div id="resizer"></div>
             <div class="coln-right" id="right">
-              <span class="show-video blink" id="switch-video"><i class="fas fa-exchange" aria-hidden="true"></i></span>
+              <span class="show-video blink" id="switch-video"><i class="fas fa-exchange-alt" aria-hidden="true"></i></span>
               <div class="collapse-video" id="collapse-video">
                   <i class="far fa-comment-alt open-chat" title="Open chat"></i>
                 </div>