Integrate nohttp

[php-coder]

We need to update the sources use https where possible and activate additional check for CheckStyle for that.

Details:

• https://spring.io/blog/2019/06/10/announcing-nohttp
• https://github.com/spring-io/nohttp
• https://github.com/spring-io/nohttp/tree/master/nohttp-checkstyle

I also have a draft with changes in Gmail.

[php-coder]

nohttp-checkstyle requires newer version of CheckStyle. So it's possibly depend on #1015

[php-coder]

I've asked Thymeleaf upstream about using HTTPS in xmlns: thymeleaf/thymeleaf-docs#76

[php-coder]

In the light of #1669 we don't need this.