Use secrets.yml rails mechanism for secrets

The `secrets.yml` is replaced upon deploy
Merge pull request #31 from alphagov/use-secrets-yml-for-secrets

Use secrets.yml rails mechanism for secrets
Send a minimal manual to the content store
Send maximal manuals to the content store

This now adds base_path to child sections.
Separate content store concerns from the input
Move base_path methods onto ContentStoreManual class

This encapsulates knowledge about the content store and the location
of manuals on GOV.UK in one place.
Send maximal manual sections to the content store

The example section had itself as a child, so we have updated the
child section's id to 123456.