www/nginx: make easier to read and maintain:

• Objectives:
  • make easier to read and maintain
  • Module config in a single section
  • use OPTIONS framwework where possible
• Add options groups for mail and http
• Use options groups to set _IMPLIES instead of large .if HTTP and MAIL blocks
• Rename all _VERSION vars to align with the OPTION name
• Add DEVEL_KIT option so we can automate
• Separate bundled and 3rd party modules
• Order options alphabetically
• Pass openssl dir to configure
• Separate external modules in separate makefile

www/nginx is buildable again with this:

• Fix sub-paths for DSO_EXTMODS introducing ${WRKSRC_mod}
• Be smarter about the if ${PORT_OPTIONS:MDSO}
• move post-install-OPT-on to where possible
• Add some OPT_NGINX_VER if used multiple times

Reviewed by: brnrd
Differential Revision: https://reviews.freebsd.org/D14773