import plugins are treated specially

I saw this in __main__.py:

https://github.com/getnikola/nikola/blob/master/nikola/__main__.py#L78

Basically, it's not looking for conf.py in parent folders if the command is init/import_wordpress/other importers

I think we should just do that for all commands that don't require configuration, but details on how to do that escape me at this point.

Doing it via a blacklist is not going to work anymore because most/all importers are going to be in the repo instead.