Also, adds Netlify CMS support for talks.

Fixes conflict between `featured` param describing if a post is featured and featured `image` param - was a typo with it also being named `featured` instead of the unique name of `image`.

Fix https://github.com/gcushen/hugo-academic/issues/1593

Adds support for writing blog posts and editing privacy policy and terms pages.

To use,
- You must already be using Netlify to deploy your site
- Login to Netlify and setup your editors under the Identity section
- Head over to YOUR_URL/admin/

See https://github.com/gcushen/hugo-academic/issues/1191