new db columns: gw_id, superevent_id, default_superevent_id. querying works
against superevent_id or gw_id.  confirm_as_gw supports data={"gw_id": "name"}
to select gw_id on creation of new gw.

1) gw_id is now a database column, not a parameter
2) gw_id can be set as a parammeter when confirming as gw
    * right now it has to be of the form GWNNNNNNA.
    * achieved with a post to superevent-confirm-as-gw-tempalte
      with optional data={'gw_id': "GW..."}
    * defaults to "old" gw_id in absense of parameter.

broken

https://git.ligo.org/lscsoft/gracedb/-/issues/199

"rety max must be less than or equal to 2", i got a little
aggressive.

1) added spiir's 'postcoh' table to the ilwd:char whitelist
2) modified contenthandler to ignore 'postcoh' table and anything
   else that can't be retrieved by TableByName

The contenthandler was inhereting changes from previous conversions.
I made uploading betwen old <--> new events more robust.

packing the LVAlert with more information: including extra_attributes
in the superevent dict --> event dict---< lvalert. It was already
included in the httpresponse.

configure space/time_coinc_far from API, incorporate
voevent changes.

modify the superevent model so that:
 1) coinc_far --> time_coinc_far
 2) new db column: space_coinc far.

These are now available as part of the API response, but the client
code needs to be modified to edit these values in updateSuperevent.

This is going to increase the size of the LVALert
packet. But from what i've seen:

https://dcc.ligo.org/LIGO-T1800079

the network can handle the traffic. I'm going to monitor
playground once it goes live there and make a judgement
call about deciding what to include in production.

by proxy it also gets added to the LVALert. This also addresses:
https://git.ligo.org/lscsoft/gracedb/issues/184

since a user can now just query an

obj['object']['preferred_event_data']['offline']

dict entry.

I still need to add some tests, and will probably have to tweak
conditional logic, but it works so far.

django 2.2.0, django-guardian-2.2.0, new search labels, caching fixes

get_from_env() stores this value as a string, but
django settings needs it as an integer. pages fail to load
otherwise!

From what i can tell, this was never implemented. Fixes this issue:

https://git.ligo.org/lscsoft/gracedb/issues/194

if the 'is_exposed' boolean is 'True', then the superevent is
public. changing the response so that it's 'is_public' would
require more than a two-line change.

In support of: https://git.ligo.org/lscsoft/gracedb/merge_requests/32

Ingests a 'FAR' field in Hz and adds it to the event data model. If
the field is present, then show it in the GRB event table on the
detail page.