Merge pull request #462 from ericsnowcurrently/backups-cleanup

Clean up the backups package.

This is intended as an idempotent change in preparation for further patches.
Add a backups config abstraction.
Add an abstraction for state-relevant paths.
Add tests for DBConnInfo.
Add a DB info abstraction for backups config.
Add tests for BackupsConfig.
Add a backups abstraction.
Add the functionality for creating a backup.
Add Create() to the backups abstraction.