Replace Transactions Explorer global 301

These mappings can't work with the Redirector, but they can work with Bouncer
which is where we'll put them.
Fix broken Transactions Explorer mappings
Add transactionalservices.alphagov as an alias

I'm not sure if we'll use it yet, but as it definitely redirects
it can't hurt to be in here.
Remove redundant mapping

This was handled by having this domain aliased.
Add Transactions Explorer tests

These cover the two variations on query params we use.
Merge pull request #455 from alphagov/replace_transactions_explorer_global_redirect_with_mappings

Replace Transactions Explorer global redirect with mappings