Revise configuration files

Revise configuration files

In response to my own usage, I find the existing fmrib.cfg overly broad and involves too many different types of processes:

1. Default processing of UKB tables using FMRIB expertise/experience/decisions
2. Selection of a large set of variables for output
3. Individual preferences; some, including high verbosity and use of extensive logging/documentation, will come down to a user's preference; some, are site-level decisions (e.g. default value for num_jobs)

In this PR I propose splitting in fmrib.cfg in the following files

• fmrib.cfg - A paired down file that just has recommended variable processing, and defines FMRIB categories (but doesn't select categories to process)
• fmrib_cats.cfg - The FMRIB categories that were previously always selected with use of fmrib.cfg
• fmrib_logs.cfg - Contains all options in fmrib.cfg, but adds maximal verbosity, logging and documentation file output.
• local.cfg - The local (maybe should be site.cfg?) that are global preferences that a local maintainer may wish to change.

This PR is really a WIP because to make use of these we really need two other modifications to funpack described in #13 (closed) and #14 (closed).