- 0052_update_gstlalcbc_O3b_cert.py: gstlalcbc was issued a new cert at CIT.
      I manually migrated on production and playground, but i'm backing up the
      migration here.
    - 0005_add_coinc_far_and_em_type.py: snapshotting the migration for the new
      `em_coinc` and `em_type` data fields. This will most likely change.

Not sure why these were generated. The models were not modified,
but maybe it was just because we are now using Python 3, and string
handling has changed compared to Python 2.  I think all of the fields
that were touched have strings in them either as a default option
or as a set of choices.

* Switch from VOEventLib to voevent-parse due to significant
  string-bytes issues in VOEventLib
* Remove bad exception handling in events API for creating a
  VOEvent
* Add parameter checking to events API for creating a VOEvent
* Combine VOEvent building code for events and superevents into
  a single instance which handles both cases

Remove usage of .keys(), .has_key(), and .iteritems(), and
account for the fact that .values() produces an iterator in Python 3.

only required on python2, but this code will break on python3 anyway

Display the "RETRACTED" part first.

We now try to get the skymap filename from the latest non-retraction
VOEven and find a related PNG file. If that fails, try to find
bayestar.png. And if that fails, don't show a skymap.

Found a few more edge cases when applying this in production,
so I'm patching this migration retroactively.

Now there are two separate steps - get notifications and
get contacts for those notifications. Makes testing easier.

Some improvements and cleanup to SupereventPublic