Add the admin app to the Procfile and Pinfile
Merge pull request #511 from alphagov/add-admin-to-procfile

Add the admin app to the Procfile and Pinfile
Move requirement of libffi-dev into common

As development, frontend, backend and jumpbox now require libffi-dev
(for SNI in python2) I thourhg moving it into common would make sense.
Merge pull request #512 from alphagov/add-libffi-to-backend

Move requirement of libffi-dev into common