Assorted changes so import hooke.plugin works ;).

Assorted changes so import hooke.plugin works ;).

Uncommenting the cut entry in PLUGIN_MODULES exposed a number of bugs
which I fixed:
  * def Plugin (object): -> class Plugin (object):
  * plugin initialization must occur *after* Command/Argument definition.
    That way the neccessary classes are defined when we go to load the
    plugin modules.
  * Broken default_settings() fixed.

Also did some docstring cleanup.