Module specific logging

**Is your feature request related to a problem? Please describe.**
A some point we are no longer going to want all logging details being sent to the same place, as it will end up being very hard to read. It seems a natural division to split logging up by module, e.g. so there is a specific plant module log that can contains all the details relevant to the running of the plant module.

**Describe the solution you'd like**
In the configuration the user can specify an output file path for each module log. Each module has a separate logger object defined, which is written to and output using the file path provided. If no file path is provided module specific logging isn't set up, and the logging details for the module will instead be written to the global logger.

**Describe alternatives you've considered**
Could stick with global logging, but suspect this will be quite a lot of effort to keep sensibly ordered.

No files, tests, or entry points are named. Start by locating the configuration handling and current global logging setup, then trace how module activity is logged. Done means users can configure per-module output paths, while modules without paths continue using the global logger.

Written by the indexing model from the issue text.