Move sdk structs to modules/structs (#6905)

* move sdk structs to moduels/structs

* fix tests

* fix fmt

* fix swagger

* fix vendor

modules/structs/utils.go

@@ -0,0 +1,26 @@
+// Copyright 2015 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 (
+	"net/http"
+)
+
+var jsonHeader = http.Header{"content-type": []string{"application/json"}}
+
+// Bool return address of bool value
+func Bool(v bool) *bool {
+	return &v
+}
+
+// String return address of string value
+func String(v string) *string {
+	return &v
+}
+
+// Int64 return address of int64 value
+func Int64(v int64) *int64 {
+	return &v
+}