Replace 'input-block-level' with 'form-control'

'input-block-level' was replaced with 'form-control' in v3. To get
block-level inputs, the 'form-control' class is now needed.

signin/index.html

@@ -21,8 +21,8 @@
 
       <form class="form-signin">
         <h2 class="form-signin-heading">Please sign in</h2>
-        <input type="text" class="input-block-level" placeholder="Email address" autofocus>
-        <input type="password" class="input-block-level" placeholder="Password">
+        <input type="text" class="form-control" placeholder="Email address" autofocus>
+        <input type="password" class="form-control" placeholder="Password">
         <label class="checkbox">
           <input type="checkbox" value="remember-me"> Remember me
         </label>