add method for cleaning the message database

lib/postal/message_db/provisioner.rb

@@ -63,6 +63,18 @@ module Postal
         @database.query("DROP TABLE `#{@database.database_name}`.`#{table_name}`")
       end
 
+      #
+      # Clean the database. This really only useful in development & testing
+      # environment and can be quite dangerous in production.
+      #
+      def clean
+        ['clicks', 'deliveries', 'links', 'live_stats', 'loads', 'messages',
+          'raw_message_sizes', 'spam_checks', 'stats_daily', 'stats_hourly',
+          'stats_monthly', 'stats_yearly', 'suppressions', 'webhook_requests'].each do |table|
+          @database.query("TRUNCATE `#{@database.database_name}`.`#{table}`")
+        end
+      end
+
       #
       # Creates a new empty raw message table for the given date. Returns nothing.
       #