Only add the Python 2 SNI-related requirements if using Python 2
Harmonize capitalization in links.
Show header buttons on all speakers page if there are no speakers.

We still want people to be able to import speakers if there aren't
any already, in fact, we particularly want them to be able to!

The nicest way I can think to do this is to include the normal buttons
from the header. It seems a bit cluttered with the 'All Speakers' heading
though, so I've taken that out until there are some.
Move instance home buttons to sayit.

These buttons used to live in the template in sayit.mysociety.org,
for reasons no-one can remember.