Add Storj DCS backend and deprecated Tardigrade DCS backend.
Storj renamed their "Tardigrade Decentralized Cloud Storage" product to "Storj DCS". This adds a new Storj DCS backend and deprecates the old Tardigrade one. A warning is issued to inform Tardigrade users to modify their configurations to use the new backend.
This also adds a passphrase verification field to ensure that the user has provided the correct encryption passphrase.
