GUACAMOLE-723: Display warning icon when background connection disconnects due to an error.

guacamole/src/main/webapp/app/client/templates/guacClientPanel.html

@@ -6,7 +6,8 @@
 
     <!-- List of connection thumbnails -->
     <ul class="client-panel-connection-list">
-        <li ng-repeat="client in clients | toArray | orderBy: [ '-value.lastUsed', 'value.title' ]" class="client-panel-connection">
+        <li ng-repeat="client in clients | toArray | orderBy: [ '-value.lastUsed', 'value.title' ]"
+            ng-class="{ 'error' : hasError(client.value) }" class="client-panel-connection">
             <a href="#/client/{{client.value.id}}">
                 <div class="thumbnail">
                     <guac-thumbnail client="client.value"></guac-thumbnail>