GUAC-1260 Allow extensions to override guacamole icons.

guacamole/src/main/webapp/app/login/styles/dialog.css

@@ -83,8 +83,11 @@
 
 .login-ui .login-dialog .logo {
     display: block;
-    max-width: 3em;
     margin: 0.5em auto;
+    width: 3em;
+    height: 3em;
+    background-size: 3em;
+    background-image: url("images/guac-tricolor.png");
 }
 
 .login-ui.continuation div.login-dialog {

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

@@ -31,7 +31,7 @@
             <form class="login-form" ng-submit="login()">
 
                 <!-- Guacamole version -->
-                <img class="logo" src="images/guac-tricolor.png" alt=""/>
+                <div class="logo"></div>
                 <div class="version">{{'APP.NAME' | translate}}</div>
 
                 <!-- Login message/instructions -->

guacamole/src/main/webapp/index.html

@@ -5,9 +5,9 @@
         <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0, user-scalable=no, target-densitydpi=medium-dpi"/>
         <meta name="mobile-web-app-capable" content="yes"/>
         <meta name="apple-mobile-web-app-capable" content="yes"/>
-        <link rel="icon" type="image/png" href="images/guacamole-logo-64.png"/>
-        <link rel="icon" type="image/png" sizes="144x144" href="images/guacamole-logo-144.png"/>
-        <link rel="apple-touch-icon" type="image/png" href="images/guacamole-logo-144.png"/>
+        <link rel="icon" type="image/png" href="images/logo-64.png"/>
+        <link rel="icon" type="image/png" sizes="144x144" href="images/logo-144.png"/>
+        <link rel="apple-touch-icon" type="image/png" href="images/logo-144.png"/>
         <link rel="stylesheet" type="text/css" href="app.css">
         <title ng-bind="page.title | translate"></title>
     </head>