Add task to republish political content
Add task to republish political content

Editions that are `political: true` need to be republished following the
election if we update the government record. This will enable history
mode on that content and display the 'Published under' banner.

This commit adds a rake task to facilitate this.

alphagov/whitehall,alphagov/whitehall,alphagov/whitehall,alphagov/whitehall