Rename mainstream browse category

This adds a data migration which renames the "Oil and gas: Exploration 
and development" mainstream browse category to "Oil and gas: Exploration 
and production".
Assign Oil and Gas categories to detailed guides

This data migration assigns the correct oil and gas categories to 
detailed guides.

When the detailed guide is published, the script will create a new 
edition, update the categories, and force publish, adding an editorial 
remark to explain the change.

When the detailed guide has an existing edition in the draft state, the 
script will just update the categories and add a remark without 
publishing.

All changes are made as the "GDS Inside Government Team" user.
Merge pull request #1223 from alphagov/migration-oil-and-gas-content

Data migrations for Oil and Gas detailed guide content