Fix return_url generation for MP pages

becuase there's redirect magic etc going on we should use
the canonical MP URL to generate the return url
Add mini survey to list of debates for a day
Add survey question across top of debates page

Nowhere else sensible to put
move mini survey about link to save vertical space
allow user to skip current mini survey question

Sets the same cookie as answering sets so we can show them the
another question
comment out debates survey while I try and think of a better solution

At the moment it's a bit intrusive so I'm going to sit on this for a bit
while I see if I can think of a better place to put it