Commit missing render template and update browser export for associated_datasets

[cmungall]

Problem

render.py loads a Jinja2 template via self.env.get_template("community.html") from src/communitymech/templates/, but that directory and template file were never committed. Running just gen-html currently fails with a TemplateNotFound error.

Request

@realmarcin — it looks like src/communitymech/templates/community.html exists on your local branch but wasn't pushed. Can you commit and push it? Once it's in, I'll extend it to render the new associated_datasets section and update browser_export.py to match.