Update to Django 2.2

Upgrade site and modules to Django 2.2. Remove and replace obsolete
functionality with current equivalents. Update requirements to latest
versions where possible. Remove unused dependencies.

Improve proposal/review styling

Use correct block for page titles. Fix element styles to be consistent
across site. Use fluid layout for review to enable sidebar.

More dashboard and settings themes (#29)

* Proposals forms now have a header panel

* Adds panels to the speaker forms

* Imports latest pinax accounts templates

* speakers/base and proposals/base now derive from utility_page.html

* Most login forms now derive from take flight themes

* Missed email_confirm

* More accounts bits

* Restructures login form

* Puts submit etc buttons inside fieldset borders

Refactors all speaker-facing forms and editing pages to use the new theme (#27)

* Themes speaker_edit.html

* speaker_create now uses takeflight theme

* proposal_submit_kind now uses takeflight theme

* fixes bug in form_snippet

* Optimises proposals_submit_kind

* proposal_submit now uses wagtail theme

* Proposal_edit now uses new theme

* More forms

* Proposal details page now loads from take flight theme

* proposal_fields now looks nicer under the take flight theme

* proposal_speaker_manage rethemed