Add support for temp usernames and an interstitial to confirm username

When a user now logs in for the first time for any external auth (LDAP, JWT, Keystone, Github, Google, Dex), they will be presented with a confirmation screen that affords them the opportunity to change their Quay-assigned username.

Addresses most of the user issues around #74

static/js/pages/update-user.js

@@ -0,0 +1,80 @@
+(function() {
+  /**
+   * Update user page.
+   */
+  angular.module('quayPages').config(['pages', function(pages) {
+    pages.create('update-user', 'update-user.html', UpdateUserCtrl, {
+      'title': 'Confirm Username'
+    });
+  }]);
+
+  function UpdateUserCtrl($scope, UserService, $location, ApiService) {
+    $scope.state = 'loading';
+
+    UserService.updateUserIn($scope, function(user) {
+        if (!user.prompts || !user.prompts.length) {
+            $location.path('/');
+            return;
+        }
+
+        $scope.state = 'editing';
+        $scope.username = user.username;
+    });
+
+    var confirmUsername = function(username) {
+        if (username == $scope.user.username) {
+            $scope.state = 'confirmed';
+            return;
+        }
+
+        $scope.state = 'confirming';
+        var params = {
+            'username': username
+        };
+
+        ApiService.getUserInformation(null, params).then(function() {
+          $scope.state = 'existing';
+        }, function(resp) {
+          if (resp.status == 404) {
+            $scope.state = 'confirmed';
+          } else {
+            $scope.state = 'error';
+          }
+        });
+    };
+
+    $scope.updateUsername = function(username) {
+        $scope.state = 'updating';
+        var data = {
+            'username': username
+        };
+
+        ApiService.changeUserDetails(data).then(function() {
+          window.location = '/';
+        }, ApiService.errorDisplay('Could not update username'));
+    };
+
+    $scope.hasPrompt = function(user, prompt_name) {
+      if (!user.prompts) {
+        return false;
+      }
+
+      for (var i = 0; i < user.prompts.length; ++i) {
+        if (user.prompts[i] == prompt_name) {
+          return true;
+        }
+      }
+
+      return false;
+    };
+
+    $scope.$watch('username', function(username) {
+        if (!username) {
+            $scope.state = 'editing';
+            return;
+        }
+
+        confirmUsername(username);
+    });
+  }
+})();