Compile task list for Django 1.11 upgrade

[jwalgran]

• Incorporate the dependency compatibility analysis from Urban Apps (Cicero)
• Research all dependencies for compatibility
• Include removing pending edits as a task
• Review deprecation notes from Django 1.9, 1.10, and 1.11

[maurizi]

Dependencies that will/may need to be updated:

• [ ] django-apptemplates - supports 1.10, unclear if it does or doesn't support 1.11
• [ ] django-contrib-comments - we're on version 1.7.3, 1.8 supports Django 1.11. No breaking changes.
• [ ] django-hstore - Doesn't support Django 1.10+ and is currently unmaintained. We switched away from using it in https://github.com/OpenTreeMap/otm-core/pull/3124 but it is still in our requirements.txt and is referenced from a migration. Do we need to squash migrations to update?
• [ ] django-js-reverse - supports 1.10, unclear if it does or doesn't support 1.11
• [ ] django-queryset-csv - supports 1.10, unclear if it does or doesn't support 1.11
• [ ] django-redis - we're on version 4.4.4, 4.8.0 is the latest and appears to support Django 1.11. No listed breaking changes.
• [ ] We're currently using django-registration-redux 1.4. There seems to be support for Django 1.11 in the latest release (1.6), but there are breaking changes
• [ ] django-statsd-mozilla - No Django 1.9+ support (!!!). Upcoming 0.4 release should 1.11+ support once it is released (https://github.com/django-statsd/django-statsd/issues/97)
• [ ] django-storages - we're using version 1.5. There is support for Django 1.11 in the latest release (1.6), but there are breaking changes
• [ ] django-threadedcomments - supports 1.10, unclear if it does or doesn't support 1.11
• [ ] django-url-tools - doesn't support Django 1.9+, currently unmaintained.
• [ ] django-tinsel has changes awaiting review to support 1.10+
• [ ] django-webpack-loader - we're on 0.3.3, curent version (0.5) lists support for Django 1.11
• [ ] rollbar - master branch has an unreleased commit fixing a deprecation warning for Django 1.10. Unclear if we need to upgrade, but probably a good idea regardless

[maurizi]

Code changes we'll need to make:

Django 1.8 deprecations:

• template settings have changed to support Jinja2 as a built-in templater, and we'll need to migrate to the new settings names. (everything is now nested under TEMPLATES)
• option_list is deprecated in management commands, so we'll need to update all of our built-in management commands
• GeoQuerySet aggregate methods have been replaced with standalone functions that work with aggregate(...), and GeoManager in general is deprecated in favor of stand-alone functions & __fn=... lookups

Django 1.9 deprecations/removals/changes:

• There are now built-in password validators we may want to consider using
• We may want to switch our test scripts to use parallel tests
• AbstractBaseUser moved locations, so we'll need to update our AbstractUniqueEmailUser subclass
• The PostGIS DB backend was renamed
• compilemessages & makemessages now automatically work on all Django apps, so we should update docs/scripts for i18n
• Paginator.page_range now returns an iterator instead of a list, which will likely require updating the custom templatetag we use with Paginators
• RequestSite and get_current_site have been moved
• request.REQUEST (which was deprecated for several versions) has been removed.

Django 1.10 deprecations/removals/changes:

• There is now built-in full text search / fuzzy string matching support, so we may want to switch to that in the importer
• CSRF tokens now changes on every request, we may need to handle this when making AJAX requests for HTML partials
• get_prep_lookup & get_db_prep_lookup (used by our internal JSONField) methods have been removed in favor of custom lookup classes. We'll need to switch to those (or switch to the new built-in JSONField)
• subclasses of AbstractBaseUser are now required to call super() in their clean() methods.
• model_to_dict, used by our Dictable mixin now handles ManyToMany fields differently and will need to be tested
• User.is_authenticated & User.is_anonymous are now properties instead of methods

Django 1.10 deprecations/removals/changes:

• Template.render no longer supports Context or RequestContext as a parameter, only dict is supported.
• We'll need to check for thread-safety in our custom template tags, or disable cached_template_loader