重构自动化代码，修复皮肤bug (#1355)

* 增加读取ast方法和AddImport 方法来增加引用包功能

* 增加在指定方法中添加头部声明global.DB业务库的方法

* 增加了自动添加AutoMigrate方法。

* 将自动化产生自动迁移功能替换为新ast

* 增加了自动注册router块的功能

* 废除旧的对router和gorm的处理方法，替换为新的自动化方法

* 修复开发模式下皮肤失效的问题

server/resource/autocode_template/subcontract/api_enter.go.tpl

@@ -1,7 +1,4 @@
 package {{ .PackageName }}
 
 type ApiGroup struct {
-	// Code generated by github.com/flipped-aurora/gin-vue-admin/server Begin; DO NOT EDIT.
-
-	// Code generated by github.com/flipped-aurora/gin-vue-admin/server End; DO NOT EDIT.
 }

server/resource/autocode_template/subcontract/router_enter.go.tpl

@@ -1,7 +1,4 @@
 package {{ .PackageName }}
 
 type RouterGroup struct {
-    // Code generated by github.com/flipped-aurora/gin-vue-admin/server Begin; DO NOT EDIT.
-
-	// Code generated by github.com/flipped-aurora/gin-vue-admin/server End; DO NOT EDIT.
 }

server/resource/autocode_template/subcontract/service_enter.go.tpl

@@ -2,8 +2,5 @@ package {{ .PackageName }}
 
 
 type ServiceGroup struct {
-    // Code generated by github.com/flipped-aurora/gin-vue-admin/server Begin; DO NOT EDIT.
-
-	// Code generated by github.com/flipped-aurora/gin-vue-admin/server End; DO NOT EDIT.
 }