redirector is now transition-config

This is the smallest change that will allow this to keep working.
Bigger change to come later.
Update comments to reflect new name for redirector

Also to reflect that we don't import mappings from redirector any more (and
haven't for a long time).
Rename some methods containing redirector

These were either no longer accurate or misleading - the hits import dealt with
hits from pre-transition logs and from post-transition logs - or no longer fit
the new name for the repo. Plus these names are shorter, which is nice.

Conflicts:

	lib/transition/import/site_yaml_file.rb
Rename data/redirector to data/transition-config

If you already have this checked out, you can do one of two things:
* run `bundle exec rake notmodules:sync` to fetch it cleanly
* run `mv data/redirector data/transition-config`
Merge pull request #460 from alphagov/rename_redirector

Rename redirector