Add chefignore file

Prevents unnecessary items from being uploaded to the Chef Server
Use HTTPS for community Berkshelf API server
Add our own Berkshelf API server, remove unnecessary entries
Use et_rails_app ~> 3.2.0 to gain context improvements

See:

* evertrue/et_rails_app-cookbook@2c577bd8dd7c
* evertrue/nginx-cookbook@fbdda22f74ce
Fix syntax in CHANGELOG to be Stove-compatible