Combine "handler" functions for the JobsAPI in tracker package

[stephen-soltesz]

Previously the handler implementations for the JobsAPI was split across two packages. This change moves all handler functions to the tracker/handler.go

Previously the instance relationships looked like:

• monitor contains a tracker
• handler contains a tracker (with three resource definitions /update, /heartbeat, /error)
• jobservice contains a tracker and config (with one resource definition /job)

With this change, the instance relationship look like:

• monitor contains a tracker
• jobservice contains config
• handler contains a tracker and jobservice (with all four resource definitions)

This consolidation (all handlers in one place) will allow us to introduce a "v2" api that extends the Job interface between the ETL parsers and the gardener.

NOTES:

• These resources are invoked using code in the etl-gardener/client/client.go package and custom implementations in etl/active/poller.go. These implementations should be consolidated to the client package in a future PR.

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This change is 

[coveralls]

Coverage increased (+0.06%) to 60.625% when pulling bfaea421730e515f2a81a827862be82362b1f0aa on sandbox-soltesz-combine-handlers into 87a3bb0f7847155d9402a48d1f8ffe4c64c8c7c1 on master.