Move sdk structs to modules/structs (#6905)

* move sdk structs to moduels/structs

* fix tests

* fix fmt

* fix swagger

* fix vendor

modules/structs/user.go

@@ -0,0 +1,38 @@
+// Copyright 2014 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package structs
+
+import (
+	"encoding/json"
+)
+
+// User represents a user
+// swagger:model
+type User struct {
+	// the user's id
+	ID int64 `json:"id"`
+	// the user's username
+	UserName string `json:"login"`
+	// the user's full name
+	FullName string `json:"full_name"`
+	// swagger:strfmt email
+	Email string `json:"email"`
+	// URL to the user's avatar
+	AvatarURL string `json:"avatar_url"`
+	// User locale
+	Language string `json:"language"`
+	// Is the user an administrator
+	IsAdmin bool `json:"is_admin"`
+}
+
+// MarshalJSON implements the json.Marshaler interface for User, adding field(s) for backward compatibility
+func (u User) MarshalJSON() ([]byte, error) {
+	// Re-declaring User to avoid recursion
+	type shadow User
+	return json.Marshal(struct {
+		shadow
+		CompatUserName string `json:"username"`
+	}{shadow(u), u.UserName})
+}