Adds db install / uninstall

#fixes #50 

Adds `message_broker_producer` database table.

**To test**
- Disable -> uninstall / re-install module.
- Check for `message_broker_producer` table in database.
  - `vagrant@dev:/var/www/vagrant/html$ drush sql-cli`
  - `use dosomething`
  - `show tables`
  - `explain message_broker_producer`
- Disable -> uninstall again to confirm database is removed.

**Note**: Your local vagrant database installation will have to be rebuilt after testing as all of the message_broker_producer variable settings will be removed in the uninstall step.

**Double Note**: As suggested by @aaronschachter , this pull request will need to be tested as an update rather than in uninstall/install to confirm support of the upgrade path that will be used by the DS affiliate sites.

Related:
#32 
Shouldn't redefine this.  Can call `message_broker_producer_schema` to get the table definition and pass the correct array to `db_create_table`.