MarkdownColumn should accept markdown configuration

[jace]

A markdown column may specifically need to allow sanitized HTML, or be pure Markdown, or something else of a variety of configuration options allowed by the Markdown processor.

1. Class MarkdownComposite accepts an options={} parameter as the last item
2. Class MarkdownColumn also accepts options={} (position irrelevant, but last for consistency)
3. MarkdownColumn calls composite with functools.partial(MarkdownComposite, options=options)
4. MarkdownComposite.__setattr__ calls markdown(value, **self.options) (pending change in Markdown processor in Replace GFM module with JS version #182)

[jace]

Related: Google has augmented rel="nofollow" with a new value ugc to indicate user generated content. This should be configurable by column or possibly by form.

[jace]

Turns out composite won't accept partial(MarkdownComposite) as a composite class.