- Add RenderedContent model and related helper methods
- Change StaticContentView `get()` logic to try the cache, then the db, then S3
- Change StaticContentView to update db appropriately
- Refactoring for readability/maintainability
- Make web service depend on redis
- Add function to extract body from html content
- In view, extract body before returning converted ascciidoc in response
Includes these failing tests:
```
=============================== short test summary info ================================
FAILED core/tests/test_renderer.py::test_get_s3_keys - AssertionError: assert '/site/develop/tools/auto_index/index.html' in []
FAILED core/tests/test_views.py::test_static_content_template_view[/site/develop/rst.css] - django.http.response.Http404: Page not found
```