Add user api registration queue and user api campaign activity

Fixes #15 

See also:
https://github.com/DoSomething/message-broker/issues/35
https://github.com/DoSomething/message-broker/issues/22

- Adds userAPIRegistrationQueue and userAPICampaignActivity queues 
- Produces entries to the queue
- Moves all exchange and queue settings to system variables and related admin forms elements. Configuration values are administered from the admin interface rather than in code.