[epilogue] Allow individual data loggers to have configurable logging levels

[SamCarlberg]

Epilogue allows users to specify the importance of individual logged fields, which the generated loggers will compare against the runtime-configured minimum importance level. This allows certain groups of data to be conditionally logged or not, but it does not allow individual loggers in multi-logger setup to have different logging levels (for example, users may not want to log low importance data to NT to save on bandwidth, but still log it to disk).

This could be implemented by adding and importance level argument to data loggers log methods, and passing in the importance level of the logged fields. Data loggers would need to be configurable with a minimum importance level; the global configuration can be kept, since it's useful as a fallback and to prevent expensive calls to retrieve unimportant data