Render archiving explanations as govspeak.
Merge pull request #1895 from alphagov/govspeak-in-archiving-explanations

Render archiving explanations as govspeak.
Fix redirects on existing Unpublishings.
Tweak data migration logging output
Parameterise whitehall public root

This ensures the data migration does the right thing, regardless of the
environment it is run in.
Repair alternative urls with stray whitespace

At least 4 Unpublishings have alternative urls with a stray whitespace at the
beginning. This will remove any stray whitespace.
Merge pull request #1894 from alphagov/fix-unpublishings

Fix redirects on existing Unpublishings.