offer default ProcessingModules named "behavior", "ecephys", etc.

[bendichter]

Feature Request

In an effort to help usability and to encourage best practices, we should offer default processing modules. This will require the following:

• a (non-breaking) schema change adding optional ProcessingModules to /processing.
• helper API functions for easily accessing these ProcessingModule objects.

My preferred syntax for the API change would be that nwb.processing.behavior would return the ProcessingModule named behavior if it exists, and if it does not exist pynwb would automatically create that module and return it.

Checklist

• [x] Have you ensured the feature or change was not already reported ?
• [x] Have you included a brief and descriptive title?
• [x] Have you included a clear description of the problem you are trying to solve?
• [x] Have you included a minimal code snippet that reproduces the issue you are encountering?
• [x] Have you checked our Contributing document?

[rly]

I am in favor of default names, but we should be internally consistent. Within the general group, there are already the names extracellular_ephys, intracellular_ephys, etc. Whichever we pick, I think they should be consistent.

[rly]

See related https://github.com/NeurodataWithoutBorders/nwb-schema/issues/249