Add new client event type - between complete and success

There is a desire to have a new client event - coming between complete, and
success. While success is the event thrown when all the incoming commands are
successfully executed, it would be useful to have an event after **each** incoming
command is executed.

There would of course need to be additional information in the data payload of
this event: id effected, presumably, as well as the name of command executed
(update, eval, etc.) Maybe more? TBD.
#### Environment
Operating System: All
Platform: All
#### Affected Versions
[2.0]

Start by tracing the client event lifecycle around the existing complete and success events. Review how incoming commands and event payloads are represented, then determine the required per-command event data and its completion criteria; the issue does not name specific files or tests.

Written by the indexing model from the issue text.