Reformat repository using new nixfmt-rfc-style.
Instead of having to manually stub packages that should not be downloaded we instead automatically stub all packages (except a small list of whitelisted ones). Tests can re-introduce the real package by using the `realPkgs` module argument.
Add a module for pandoc that provides the following: 1. Setting default configuration options. 2. Installing templates. 3. Installing citation styles.
