Refactors codebase

Refactors duplicated code. Renames and reorganizes classes and methods.
Refactors tests.
Kafka message handling is removed from plugins. They now return response msg
dict and top level code handles publishing.

Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>
Change-Id: I9826db9c4586d961f40af6cb194fc388fe855ae1