documentation

Pull request #2043: feature/DEV-3386-7.2-D38a. moved frontend pre-requisites to "Requirements" page (sub-issue 38).

Merge in WEB/documentation from feature/DEV-3386-7.2-D38a to release/7.2

* commit 'd64575c56116d674b9d2bf66093fb9869c661aed':
  [DEV-3386] updated table formatting (sub-issue 38)
  [DEV-3386] updated table formatting (sub-issue 38)
  [DEV-3386] updated table formatting (sub-issue 38)
  [DEV-3386] updated table formatting (sub-issue 38)
  [DEV-3386] moved PHP options back to frontend.md (sub-issue 38)
  [DEV-3386] improved section structure (sub-issue 38)
  [DEV-3386] reverted section heading (sub-issue 38)
  [DEV-3386] added missing PHP option (sub-issue 38)
  [DEV-3386] fixed link (sub-issue 38)
  [DEV-3386] restored introduction for frontend requirements/pre-requisites table (sub-issue 38)
  [DEV-3386] moved frontend pre-requisites to "Requirements" page (sub-issue 38)