Cabinet Ministers can be paid/unpaid and also attend cabinet

Split the ministers who attend cabinet out into their own section.

footnotes should only be added to one of the roles or they will show
twice if a person holds two roles
Role unit test
functional test for also_attends_cabinet roles
Cucumber test and change id of the also-attends-cabinet
Data migration for the roles

from http://www.number10.gov.uk/the-coalition/the-government/