Pupa

Improvements:

* Add `pupa clean` command to delete database objects that haven't been seen in recent scrapes

Improvements:

* allow null event locations
* resolve memberships based on start date, falling back to end date if no start date is available

Fixes:

* raise exception for whitespace in urls

Improvements:

* fire post-save hook on imports
* check family_name when resolving names

Fixes:

* if scrapers are omitted on command line, use all scrapers again

Improvements:

* add data quality reports that update after each import (requires migration)
* add flags to disable person, bill, vote, event import
* let date be set on event media & document

Fixes:

* Fix warnings from obsolete usage of importlib & jsonschema
* remove parties from tests
* don't call check_session_list if running import only
* add support for Post.maximum_memberships
* add support for Person given & family names
* stop testing on Postgres 9.x

Fixes:

* minor packaging fixes & dependency pinning tweaks

Backwards-incompatible changes:

* fix_bill_id is no longer called on bill identifiers

Improvements:

* django 2.0 compatibility fixes (on_delete on models)
* require python-opencivicdata 2.1 fixes
* drop validictory for jsonschema
* add 'pupa party' command for atomic addition of parties, deprecate Jurisdiction.parties
* add IMPORT_TRANSFORMERS setting allowing alterations of data on import

Fixes:

* bugfix for OrganizationImporter other_names
* bugfix for VoteEvent bill resolution
* bugfix for VoteEvent bill action resolution (307)