Made Scaffold work as a Virtualenvwrapper's project base template

[virtualenvwrapper](http://virtualenvwrapper.readthedocs.org) is an excellent (set of) tool(s) to facilitate the work with the essential [virtualenv](http://www.virtualenv.org/en/latest/).

I've just give a simple support to run Scaffold though the `project.template` hook, so you can run:

    $ mkproject -t base newproject 

Note that virtualenvwrapper isn't mandatory.