增加loading；修改部分css

frontend/admin/index.html

@@ -1,11 +1,14 @@
 <!DOCTYPE html>
 <html>
-  <head>
+<head>
     <meta charset="utf-8">
     <title>Online Judge Admin</title>
-  </head>
-  <body>
-  <div id="app">
-  </div>
-  </body>
+</head>
+<body>
+<div class="cssload-battery">
+    <div class="cssload-liquid"></div>
+</div>
+<div id="app">
+</div>
+</body>
 </html>