Adds alarm engine

Adds alarm engine

Alarms are now created directly through mon-central. A new component called
mon-evaluator evaluates the alarms and sends a notification in case it
triggers. Alarms are still created through the Kafka bus using the same model.

It also deletes all of the old unused code of the plugin model. There were
thousands of lines dedicated to provide CRUD operations for metrics and alarms
in the VIM plugins that were never used. MON only requires to collect metrics
and insert them in the TSDB. VIMs manage their metrics autonomously. The tests
for that were also removed. This was done to make the codebase more
manageable. Support for VROPS and AWS will be added in a future patch. Neither
of those two plugins worked correctly. They need to be adapted to the new
consumer plugin model.

Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>
Change-Id: I656c78be82ca21b760a83b478560d0c8ae680222