Refactor the initializer.

There is still some redundancy, but I think this makes
it easier to add new initialization parameters in the future.

Also, removing the Loggable and Configurable roles simplified
things overall.
Update to match new Initializer interface.
Remove the 'devel' configuration attribute, since we're not using it.

But this may come back in the future when we know what it should do.
Remove Mailrc class.

This is only used by the Initializer, and it is so small
that it hardly seemed worthy of a separate class.
nohistory is now no_history.
Tweak documentation strings for config values.
Renamed File::Modlist -> ModlistWriter.

It has a similar name and interface as the IndexWriter.