Assorted fixes (#47)

* Invokes the site tree fix from previous fixes.

* Adds a disclaimer noting that previous years’ accounts have not been carried over.

Fixes #43

* Adds proposal type to the proposal summary page.

Fixes #40

* Adds travel/accommodation assistance to the proposals page, but makes it only visible to speakers in the proposal, or review managers.

Fixes #41.
Fixes #42.

* Reduces a lot of the whitespace in the header and footer.

Fixes #44

* Proposals review page now shows information for every speaker on a proposal.

Fixes #45

* Makes sure that non_field_errors are displayed by forms.

Fixes #37

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