refs https://github.com/TryGhost/Team/issues/946
This adds the initial bulk actions endpoint used for the members
filtering feature. The idea is to eventually move bulk destroy into this
endpoint to and provide a consistent interface for applying bulk actions
to members.
The @tryghost/members-api package has been bumped to include the new
bulkEdit method.
The sinon.restore in tests was moved to an afterEach so that stubs did
not effect other tests.
