0.4 doc updates

Proofed the entire Aperture Tiles site to clean up formatting and fix outdated references to code.

Still have a few things to add:

- Reconcile outdated Client-Side Rendering code block on the Docs > Development > Configuration page
- Update Docs > Development > Quick Start and Generation pages to replace outdated spark-run script information 
- Pull in latest changes to API docs (probably part of a PR for api-docs-update-v2 branch)
- Update links on Download page for new packaged distributions
- Update screenshots in User Guide, if time allows