How to have a version control in django?

I have Django webapp with different content (e.g. Posts, Threads, comments) and I want to keep track of their history. So I'm trying to create a "version-control" for "content". This is how I'm doing it (skip to the end for the question):

I have a model Create_Content which represents an action: has an actor (editor), a set of modifications (edition), a timestamp, and the content it acts on:

class Create_Content(models.Model):
    editor = models.ForeignKey('User')
    edition = models.TextField() # pickled dictionary
    date = models.DateTimeField(auto_now_add=True)
    content = models.ForeignKey('Content')

which is saved exactly once because history cannot be changed.

I define content has:

class Content(models.Model):
    last_edit = models.ForeignKey(Create_Content, related_name='content_last_id')
    first_edit = models.ForeignKey(Create_Content, related_name='content_first_id')

    def author(self):
        return self.first_edit.editor

where last_edit is the last action performed it, and first_edition I use to get the initial author of the content.

All the actual content of the webapp is implemented by derived models of Content, which are created/edited by derived models of Create_Content. For instance,

class Comment(Content):
    post = models.ForeignKey(Post, related_name="comment_set")
    body = models.TextField()

is created during the save of Create_Comment(Create_Content) (in fact all subclasses of Create_Content are proxies).

For instance, user editions are instances of a subclass of Create_Content (e.g. Edit_Comment(Create_Content)) which, during save(), makes last_edit to point onto self and updates the actual content (e.g. Edit_Comment.body<