Repo size in admin panel (#1482)

* Implementation of the feature to view repository size in admin panel
 * Move GetRepoSize to git module
 * Repository.RepoSize -> Repository.Size
 * RepoSize -> Size in template
 * Redo a few bits and pieces
 * Update size when syncing mirror or forking
 * Remove GetRepoSize
 * Changed fatal errors to error message

* Copy migration code from Gogs

* make fmt

modules/templates/helper.go

@@ -82,6 +82,9 @@ func NewFuncMap() []template.FuncMap {
 		"DateFmtShort": func(t time.Time) string {
 			return t.Format("Jan 02, 2006")
 		},
+		"SizeFmt": func(s int64) string {
+			return base.FileSize(s)
+		},
 		"List": List,
 		"SubStr": func(str string, start, length int) string {
 			if len(str) == 0 {