Add statements printing on debug output

Display the statement being applied on the debug output, as it may be
handy to have them recalled.
Add UnsetMigrationApplied to the service interface

Unsetting the applied migrations (removing them from the migration table)
is needed by the remove command
Add the reverse command

Add a reverse subcommand to the main command, as the logical oposite
to the apply command and the last feature necessary for an equal level
of functionality with the current live version.
Fix configuration tests error incurred by the Env method refactor

The Env method was moved from configuration.Env to configuration.Configuration.Env
and it signature changed, but the unit tests weren't adapted to this new
structure. It is now done.