fix remaining Thor warnings in specs

- Thor::Actions unneeded
- launch decrypt commands with exec()
create paths only if needed
add `backup check` command
misc CLI cleanup
update examples

- Changes in final backup package paths for Databases
- New `encryption` setting for Notifier::Mail
deprecate Database _utility methods

If the path to a utility must be specified, it should be done using
Backup::Utilities.configure in the config.rb file.