Migrate netlify-cms-www site into this repo (#860)

* Add frontmatter to docs files (prep to move)

* Move docs into position for website migration

* Migrate website from netlify-cms-www

Some modifications, including most of the changes in https://github.com/netlify/netlify-cms-www/pull/58 (previously reverted).

Also updated the readme and added hugo-bin for quicker onboarding of new docs contributors.

* Remove netlify.toml

This allows separate build commands for cms-demo and netlifycms.org.

* Remove website/netlify.toml

May re-add later, but it's not doing anything for now.

* Remove unused content file

website/site/data/notifications.yml

@@ -0,0 +1,16 @@
+notifications:
+  - loud: true
+    message: >-
+      Register to join us online for our next community dev meeting, every other
+      Wednesday at 9am-10am PT!
+    published: false
+    title: Netlify CMS Development Planning Sessions Promo
+    url: >-
+      https://www.eventbrite.com/e/netlify-cms-planning-session-bi-weekly-tickets-35794058994
+  - loud: true
+    message: >-
+      We have a community on Gitter - join now to ask questions and discuss the
+      project with other devs!
+    published: true
+    title: Gitter shoutout
+    url: 'https://gitter.im/netlify/netlifycms'