Role refactor (#7867)

* role refactor

* add missing file

* fix web test

app/post.go

@@ -122,7 +122,7 @@ func (a *App) CreatePost(post *model.Post, channel *model.Channel, triggerWebhoo
 	if utils.IsLicensed() && *a.Config().TeamSettings.ExperimentalTownSquareIsReadOnly &&
 		!post.IsSystemMessage() &&
 		channel.Name == model.DEFAULT_CHANNEL &&
-		!CheckIfRolesGrantPermission(user.GetRoles(), model.PERMISSION_MANAGE_SYSTEM.Id) {
+		!a.CheckIfRolesGrantPermission(user.GetRoles(), model.PERMISSION_MANAGE_SYSTEM.Id) {
 		return nil, model.NewAppError("createPost", "api.post.create_post.town_square_read_only", nil, "", http.StatusForbidden)
 	}