Edit slugs when redirecting URLs
Edit slugs when redirecting URLs

As well as redirecting from old URLs to new URLs, we will in some cases
want to change the actual slug that's being redirected _to_. This commit
changes the slug before the redirect views get to it, meaning they will
all redirect to the correct slug, even when requesting a legacy slug at
an old URL

DemocracyClub/yournextrepresentative,DemocracyClub/yournextrepresentative,DemocracyClub/yournextrepresentative