GUAC-1126: Use round, red "x" button for disconnect.

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

@@ -59,7 +59,7 @@
             <!-- Stationary header -->
             <div class="header">
                 <h2>{{client.name}}</h2>
-                <button class="close" ng-click="disconnect()"></button>
+                <button class="close danger" ng-click="disconnect()" title="{{'CLIENT.ACTION_DISCONNECT' | translate}}"></button>
                 <guac-user-menu></guac-user-menu>
             </div>