Consolidate sphinx documentation.

Changes:

• Use {CAPS WITH SPACES} for user variables.
• Update windows landing page with subpage links.
• Update style-guide with variable and link guidance.
• Update build documentation with how to check links.
• Updated ConfigTable version.
• Update sphinx build and style guide docs.
• Remove unused variables from Makefile.
• Migrate Conan Exiles / 7 Days to Die docker service.
• Removed unifi-controller VM template. Use service/unifi.
• Move Play-On to services, and remove VM templates.
• Convert Play-On requirements to ConfigTable table.
• SSH documentation moved into SSH service; references updated as needed.
• Variables standardized (e.g. USER/USERNAME).
• Consolidate glossaries to a single location.

Fixes:

• aafig does not support the CheckExternalLinksBuilder (returns format = ''); override with an explicit no output for aafig if the builder format cannot be determined. This does not change the code otherwise.
• Add explicit linkcheck option for Makefile, as specifying a custom configuration location breaks the option interpretation.
• Update link checker configuration and fix links.