Change Repo type

The old Repo type has a repoKind

    repoKind     :: Either RemoteRepo LocalRepo,

where LocalRepo was isomorphic to unit:

    data LocalRepo = LocalRepo

This commit changes Repo to

    data Repo =
        -- | Local repositories
        RepoLocal {
            repoLocalDir :: FilePath
          }

        -- | Standard (unsecured) remote repositores
      | RepoRemote {
            repoRemote   :: RemoteRepo
          , repoLocalDir :: FilePath
          }

instead, which is a little more idiomatic and will make adding more repository
types easier.