use/httpserver.rst: multiple updates

* Update config variables
    * add favicon
    * host is nowadays known as hosts4
    * add hosts6
    * move keepalive above port as that is how it appears in the bot too
    * specify that HTTPd might require port change, not HTTP
    * HTTPd might not work if port is too low = port is under 1024
* Apache is in front of Supybot's HTTPd, not behind.