Bill 37: Fix outdated documentation and incorrect docstrings (PR #293)

Submitted by: mfosterw

- Update docs/webiscite.rst to reflect current architecture: GithubWebhookView and PullRequestHandler replace the removed github_hook, process_pull, and pr_opened identifiers - Fix managers.py docstrings: correct parameter names and return descriptions for create_from_github on both managers; add missing docstrings to get_queryset and annotate_user_vote; add module docstring - Fix webhooks.py docstrings: update module docstring to class-based view; fix _validate_header and _validate_signature return type descriptions - Add missing module docstring to activitypub/models.py

Diff: +53 -28