Strip/bleach speech summary displays for title/next/previous links.
Switch tests to use PostgreSQL, same as main site.
Remove django-mptt, replace with native CTEs.

I have a nagging concern with django-mptt - having to do the rebuild()
in the test, for example - plus I worry about slow insertion as the
database grows, and general fragility/complexity. Also, wanting to
have a default insertion order display made displaying by title need
something different anyway.

So this is switching back to a simple adjacency list, using CTEs to do
recursive descendant/ancestors.
Improve display when dates provided, but not times.
Have a list of speakers on instance front page.
Add subtle horizontal rule between speeches.

Using :after in order to have a rule that is not full width,
with a negative bottom to be more nicely placed.
As we're no longer using/installing django-mptt, need to modify old migrations to not require its field, so fresh installs work.
Merge branch 'issue28-speaker-popit-bio'

Conflicts:
	speeches/tests/speaker_tests.py
Update test to use correct IDs, won't be 1 and 2 under postgres.