Add support for multiple data logging systems

[mMerlin]

The work under way is separating the process monitoring and correction code from data logging code. It will be drop in easy (configuration file entry) to replace one data logging module with another.

Extend that. Create a data logging module that does not do any logging of its own. Instead, it delegates logging to other modules. Each module could be configured differently, so state change events could be sent to one, sensor reading to another, and both to a third.

Consider what it would take to make the logging modules 're-entrant', so that a single module could be used multiple times in the same application instance. For example, the plotly logging could be set up to use multiple plot. Each could be configure to chart the information for a single sensor, and the associated controls. Instead of (or in addition to) a chart that combines all of the logged data. Or a data logging module that saves to a file could use separate files for different (sets of) events.