fixes #907
fixes #1296

* Add security headers to nginx config

Increase the security of the nginx server and the served page, by adding the following security headers to the nginx config:
- X-Frame-Options (Disables click jacking by disallowing the page to be run in a frame/iframe)
- X-XSS-Protection (Enables cross site scripting filtering)
- X-Content-Type-Options (Disables MIME sniffing and forces browser to use the type given in Content-Type.)
- Content-Security-Policy (Controls resources the user agent is allowed to load for a given page.)
- Referrer-Policy (Governs which referrer information sent in the Referer header should be included with requests made.)

Additional headers that could be added optionally:
- Strict-Transport-Security (Enforce HTTPS over HTTP)

fixes #1156

fixes #1173

fixes #1233

fixes #1247

thanks to @masatokinugawa

Co-authored-by: Jonathan Bailey <jonathan_bailey@bose.com>
Co-authored-by: Roman Hotsiy <gotsijroman@gmail.com>

fixes #1218

* sort discriminator entries by mapping order

* fix string compare

* fix: update collapseAll method
to avoid collapsing whole object/array

* fix: remove extra "slice()" call

Co-authored-by: Alef <aleksey.pavlov@corp.mail.ru>