django-autosave bug fixes and new features

- Now works on add_view in addition to change_view
- Fixes bug where ckeditor content filters causes fields to be
  incorrectly flagged as having changed (and thus erroneously showing
  the autosave prompt)
- binds to 'locking:disabled' and 'locking:enabled' events, so
  that the prompt to revert is not displayed if the form is locked.
- Adds link in prompt to reload without autosave and to discard
  the autosave. Previously the prompt instructed the user to refresh
  but doing so causes the POST data to be resubmitted and the autosave
  to be loaded again.
- Autosave data and timeout are now stored in a single localStorage key
  for simplicity.
Bump version to 0.5.3
Cleanup from code review
Fix AttributeError: datetime.datetime => datetime
Bump version to 0.5.4
Fix bug where autosave interprets all checkbox inputs as checked
Fixes to AdminAutoSaveMixin.get_form()

- ModelAdmin.get_form() passes kwargs.get('form', self.form) on to
  the modelform_factory. If we want to extend the form class returned
  from get_form() we will have better luck by passing the 'form' kwarg
  than extending the result of the ModelForm factory (or, for that matter,
  performing a deepcopy on it).
- Adds method full_clean() to IllegalForm to prevent the call to the model
  and form clean methods, as these can have side-effects. Within the extended
  method we clear out any validation errors and delete self.cleaned_data, to
  mimic these lines in the parent:

    if self.errors:
        del self.cleaned_data

  The deletion of self.cleaned_data in ModelForm.full_clean() in the case of
  ValidationErrors goes away in django 1.6. This shouldn't matter in our case
  since we want to prevent field validation anyway.
Bump version to 0.5.5
Change revert banner back to info.
Bump version to 0.5.6
Clear autosave data on form submission for add_view

If the submission is successful, and we fail to do this, the user will be
prompted to restore their previous autosave the next time they go to add an object.
Bump to version 0.5.7