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