Update Reverse-proxy configuration page

Page: https://doc.nuxeo.com/nxdoc/http-and-https-reverse-proxy-configuration/

• Section "Motivations for Virtual Hosting":
  I don't know why we use the term "virtual hosting" here, I think we're talking about reverse-proxying, which isn't the same ting.

• Section "Bandwidth and Transactions Optimizations":
  As far as I can tell, it's just plain wrong.
  This assumes the reverse proxy will fully buffer all uploads and downloads, which in most cases is not true.

• Section "Virtual Hosting Configuration for Apache 2.x
  ":
  Same thing as the first point about virtual hosting vs reverse proxying.
  I can't tell if the subsection about webengine is still correct, but I believe some of the URLs for resources have been changed? (eg themes)
  Subsection "Configuring HTTP Cache": why is it here? This has nothing to do with either reverse-proxying or Apache configuration.