Move sdk structs to modules/structs (#6905)

* move sdk structs to moduels/structs

* fix tests

* fix fmt

* fix swagger

* fix vendor

modules/structs/org_member.go

@@ -0,0 +1,10 @@
+// Copyright 2016 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
+
+// AddOrgMembershipOption add user to organization options
+type AddOrgMembershipOption struct {
+	Role string `json:"role" binding:"Required"`
+}