mcsapi needs a new read API Design

We need an ORM-style NoSQL read API to go along with the bulk write API of mcsapi.

This will likely take the form of:

1. A reader in ExeMgr which will convert messages from mcsapi into jobs
2. Code in mcsapi to send/receive the messages

Although ExeMgr can already receive messages with an execution plan the format is very complex and ABI breaks easily (we often send whole C++ objects).

We should look at other ORM frameworks for inspiration as the the API design.

This task to do the design for this API.