Ministers are paid/unpaid and can attend cabinet

Adding a new section on the ministers page for the people who also attend cabinet
Add footnotes for the different unpaid/payed types

A data migration is included to set the footnotes as per http://www.number10.gov.uk/the-coalition/the-government

https://www.pivotaltracker.com/story/show/43700499
https://www.pivotaltracker.com/story/show/43700529