Move some code into models/git (#19879)

* Move access and repo permission to models/perm/access

* fix test

* Move some git related files into sub package models/git

* Fix build

* fix git test

* move lfs to sub package

* move more git related functions to models/git

* Move functions sequence

* Some improvements per @KN4CK3R and @delvh

modules/setting/repository.go

@@ -20,6 +20,9 @@ const (
 	RepoCreatingPublic             = "public"
 )
 
+// ItemsPerPage maximum items per page in forks, watchers and stars of a repo
+const ItemsPerPage = 40
+
 // Repository settings
 var (
 	Repository = struct {