Complete tom_pittgoogle integration for Elasticc

[troyraen]

Complete the pittgoogle integration with TOM Toolkit DESC/ELAsTiCC.

• Move the tom_pittgoogle consumer to a new pittgoogle_client repo (related to Move user tutorials and pgb-utils to a dedicated repo Pitt-Google-Broker#78) (There is a new Pub/Sub consumer in-progress in Pub/Sub client pittgoogle-client#6, we should use that here...).
• Update the tom_pittgoogle brokers to use consumers from pittgoogle-client. #3
• Update the tom_desc listener to use the new Avro parser
• Debug the tom_pittgoogle broker from within tom_desc

[troyraen]

We ran successfully in the ELAsTiCC challenge using pittgoogle-client directly. Closing this issue as 'will not complete'. We should still update tom_pittgoogle to use pittgoogle-client, so opened #3.