Fixes #1740

Description

Remove jquery; cache files; add references, robots.txt, and sourcemaps

Checklist

• I have labeled my PR with: bug, feature, engineering, security fix or testing
• I have performed a self-review of my own code
• I have reviewed the title & description of this PR which I will use as the squashed PR commit message
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• I have enabled auto-merge (optional)

Testing

Testers, use the following instructions against our staging environment. Post your findings as a comment and include any meaningful screenshots, etc.

Click the links on the homepage; everything should work even without JQuery.
Run the Lighthouse report in the Chrome Developer Tools. Feedback should not include warnings about

• an invalid robots.txt file
• very many uncached items
• missing sourcemaps for main.bundle.js, manifest.bundle.js, or vendor.bundle.js