Combine multiple metadata files to 1

The individual deployment metadata files are now 1 single metadata.json
file

Correct bug where you got an error trying to add e.g. mysql to a
scalable app

Update deployment pruning algorithm so it removes the oldest deployment
by latest activation time, and then deletes any activation metadata
prior to the latest activation time of the deployment being deleted
across all deployments

Removed all rollback-related code, as rollback is the same thing as
activate