This provides the integration base class, database model and manager for extensions to implement and register integrations.
Compared to the extension framework, these integration model will provide a way for users, such as local site administrator, to manage their own individiual integration. Third-party services will need to subclass the integration base class to provide the initialize and shutdown method for their services. 
With the database model, multiple instances of the integration's configuration could be supported, and thus providing multiple configurations of the integration for a single web server. 
All these configured integration will then be managed through the integration manager.

Added unit test for the integrations.

Test manager on creating, deleting, toggling of configured integration.
Test manager on handling of invalid configured integration.

Mannual testing with a dummy integration. 
Unit tests pass.