Added get_medusa_paths method to Page

This is used to find a list of URLs for the entire site to feed into django-medusa
If your page requires extra views, you can override this like so:
def get_medusa_paths(self):
    yield '/myextraview/'
    super(MyPageType, self).get_medusa_paths()
Added medusa renderer for pages
Fixed typo
Added contrib folder
Moved medusa renders into their own app in contrib
Added medusa renderer for documents
Renamed get_medusa_paths to get_staticsite_paths
mention some more optional/required dependencies in 'getting started' docs
Added document describing how to generate a static website
Renamed get_staticsite_paths to get_static_site_paths
Added unit tests for get_static_site_paths
Added changelog entry
Merge pull request #249 from kaedroho/medusa-integration

Django-medusa
Missing underline for new static generation docs
Include static site generation docs in doc index
Rewrite get_form_types() to not require fiddling with metaclasses to populate FORM_MODEL_CLASSES
Removed stray print statement
Remove validate_usage from the wagtailforms.backends API. Since non-expert users are likely to be inheriting from AbstractEmailForm rather than hooking up backends to their own custom form models, it is of marginal usefulness and not worth the added complexity of the metaclass setup
no point in making form a property of the form page, since its scope is entirely within the 'serve' method
Replace wagtailforms.backends model with a simple inheritance model