paver create_plugin should generate a pep8-compliant project skeleton

[EliAndrewC]

Our current paver create_plugin command generates files with some non-pep8-compliant whitespace. Specifically there are some places where we don't put 2 lines before class/function definitions.

This is somewhat harder to fix than it sounds. There are a bunch of places where we do things like

{% if GENERATE_WEBAPP %}
@all_renderable()
class Root:
    ...

Generating newlines such that we end up with the correct number for all combinations of settings will take a careful eye and a bit of testing, but overall shouldn't be too bad.