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 
My understanding is that you should not use the hook_schema table definition in hook_update functions. Going forward in the modules lifecycle hook_schema may change resulting in the hook_update function breaking. Best practice is to define the schema in the hook_update function so there's always a defined upgrade path in the module regardless of the current contents of hook_schema.

Reference:
https://www.drupal.org/node/150220

> When writing hook_update_N() functions to create a new table, it seems natural and obvious 
> to use the module's hook_schema() function to access the current definition of the table to 
> avoid duplicating the table definition in the hook_update_N() function. However, you cannot 
> safely use hook_schema() from within a hook_update_N() function.