Replace gnupg packages with a single module/class

Soon to be used as a dependency by other modules.
Module for credentials store and dependencies

Replaces encfs/fuse4x package resources with proper modules, which will also
install the kext. Included new `projects::deployment::creds` for people that
have access to it and were previously installing those packages.

/cc @samjsharpe @nickstenning
Merge pull request #3 from alphagov/encfs_creds_store

Module for credentials store and dependencies