feat(auth): add an auto-focus directive and remove username placeholder

app/components/auth/auth.html

@@ -16,7 +16,7 @@
             <!-- username input -->
             <div class="input-group">
               <span class="input-group-addon"><i class="fa fa-user" aria-hidden="true"></i></span>
-              <input id="username" type="text" class="form-control" name="username" ng-model="formValues.Username" placeholder="admin" autofocus>
+              <input id="username" type="text" class="form-control" name="username" ng-model="formValues.Username" auto-focus>
             </div>
             <!-- !username input -->
             <!-- password input -->

app/components/initAdmin/initAdmin.html

@@ -36,7 +36,7 @@
             <div class="form-group">
               <label for="password" class="col-sm-4 control-label text-left">Password</label>
               <div class="col-sm-8">
-                <input type="password" class="form-control" ng-model="formValues.Password" id="password">
+                <input type="password" class="form-control" ng-model="formValues.Password" id="password" auto-focus>
               </div>
             </div>
             <!-- !new-password-input -->

app/directives/autofocus.js

@@ -0,0 +1,14 @@
+angular
+.module('portainer')
+.directive('autoFocus', ['$timeout', function porAutoFocus($timeout) {
+  var directive = {
+    restrict: 'A',
+    link: function($scope, $element) {
+      $timeout(function() {
+        $element[0].focus();
+      });
+    }
+  };
+
+  return directive;
+}]);