Refactored out an interface of the mock event service to aid testing.

AFDP-95
Altered notification center implementation to use a thread pool.

AFDP-95
Created a single-threaded mock event service to use with tests.

AFDP-95
Updated unit test to mock in the mock event service.

AFDP-95
Wired in different mock event services for production and test.

AFDP-95