Make sure the PPC importer doesn't overwrite existing data
Add more manual matches of new candidates against old
Add some more constituency name corrections
Add more human decisions about scraped PPC matches to PopIt data
Don't include people who've changed constituency in the 'not sure' section

Previously, people would only have been excluded from the "not sure"
section on the constituency page if either they're marked as standing
again in that constituency, or they're marked as not standing anywhere -
it was missing people who we know are standing in a different
constituency.

Fixes #694
Add scraped and auto-cropped PPC images
Add the unknown person icon from TheyWorkForYou
Display candidate images where available

The CSS for the candidate images is a bit ropey, but some design time
from Zarino is forthcoming.
Format warnings better and cope with non-ASCII content
Fix the finding of previous manual decisions

The logic for finding whether we already had made a decision about a
particular person was broken and missed people, so you kept getting
asked about them; this commit fixes them.
Update the submodule with scraped PPC data
float candidate images to left, new placeholders for missing images
refactor scss for candidate lists
split scss into separate files; fix .container indentation as byproduct
fix .content__inner nesting bug
Factor out generation of data for leaderboards and recent changes

This is so that these data can be used on the home page too without lots
of duplicated code.  Maybe yet another mixin isn't a great idea though :/
show top users and recent edits on homepage
sort out candidate profile page header
Merge branch '79-design-improvements-rebased'