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

Previously, core.vfile.VersionedFile inherited from file,
which is problematic for several reasons, but primarily because
file doesn't exist in Python 3. So we rework it to just be a
normal class with a file attribute, and add/change certain
methods accordingly.

Import version of urlencode which is packaged with Django in order
to facilitate Python 2-3 compatibility.

we need to dance between str (unicode) and bytes to talk to hashlib and StringIO at the same time

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

Trying to remove a label that was not associated with an event
gave a 400 HTTP response. Fixed to be 404. It was already correct
for superevents.

Add a pipeline_type field to the Pipeline model. This will facilitate
grouping of pipelines into different classes.

Data migration to populate new database columns for existing
VOEvents. We have to read the files in and try to extract the
parameter data, handling all of the changes to the file format
which have occurred over time.

I did a lot of testing by copying over the production database
and associated VOEvent files for all non-Test, non-MDC events
and superevents to make sure we are accounting for all changes
in VOEvent (file) schema that have happened over time.

We can change a few things about how the VOEvent file building
works now that all of the relevant parameters are stored in the
database.

There are several fields that the user provides to create a
VOEvent through the API, which are used in generating the VOEvent
file, but are not stored in the database. Let's fix this!!

GroupObjectPermission and data directory cleanup should only happen
*after* the event or superevent row is removed from the relevant
table.

A web view has been created which allows EM advocates to disable
or enable pipeline submissions. This is to prevent misbehaving
pipelines from submitting bad information. The mechanism works by
preventing events from being submitted to a given pipeline, not
by revoking certificates or removing user account permissions.

Previous arrangement was not including zero-valued fields. We now
include all non-None fields.