Added support to update repository data

Its important to notice that `Update` does not renames the repository, cause the `Rename` method removes the old repository in mongo, inserts the new and renames the filesystem repository. While `Update` just do a simple database update. So its important to maintain this two methods separeted to avoid an intermitent state on database in cases that one of them doesn`t works.
I think `err` should be returned instead, no?