bug 773522: Fix djcelery tables with a local migration

djcelery has South migrations, now. But, we already slapped South migrations on it in our own local directory. This means some things are broken and DB columns missing, though I don't think anyone noticed until now.

Oh yeah, and spot-checking this might be odd. Basically:

* Visit djcelery sections in the admin, expect errors in a few of the sections.

* Run `mysql -uroot kuma`
    * These tables should not exist: `celery_taskmeta`, `celery_tasksetmeta`
    * These columns should not exist: `djcelery_periodictask.description`, `djcelery_taskstate.retries`

* Run `./manage.py migrate` and expect no errors.

* Visit djcelery sections in the admin, expect that the previous errors are now fixed.

* Run `mysql -uroot kuma`
    * Check that these tables now exist: `celery_taskmeta`, `celery_tasksetmeta`
    * Check that these columns exist on the respective tables: `djcelery_periodictask.description`, `djcelery_taskstate.retries`

This PR is step 1, which brings our custom migrations back in line with djcelery's official migrations. Step 2 will be to delete our local migrations, once they've been applied, and to let djcelery manage itself going forward.