Install config file direct from internal defaults

[anoved]

We install ~/.mmserver/mmserver.conf automatically if /usr/share/mmserver/mmserver.conf is available, but run from (unmodifiable) internal defaults if neither file is present. Consider writing internal defaults to file if necessary. Include help commentary present in current default config file.

If an equivalent default config can be generated from internal default values, consider scrapping the external sample file, or at least use the auto-generated version as the sample, rather than manually maintain two defaults (file and internal).