Add a heartbeat to the Client

[AndyGrant]

Currently, we attempt to report to the server every 30 seconds or so. If we have no data, we can still hit the server in order to keep our worker "updated". At this time, the server may send a response with a "stop" header. The client then can set the abort flags on the cutechess threads.

This will resolve an issue where the framework "appears" to lose cores when playing long workloads, or tunes that have BULK reporting.

[AndyGrant]

Resolved in b3f8cc6