(filter) move pptpd rules to a temporary spot. they belong to the plugin, but before we can change the plugin this code need to be active

Credits: https://redmine.pfsense.org/issues/4111

(menusystem) it's ok to link to an item on the page, as long as we don't try to match it back on the server end

192.254 is a legal IPv4 range.
169.254 is the correct private IPv4 address space.
Moved the order of the private address.

PR: https://forum.opnsense.org/index.php?topic=3884.0

Prodded by weust on IRC, let's just make this redirect to the
firmware page on link click abandoning the need to cache the
update info in a suboptimal way.

o consolidate "unbound_" prefix for unbound.inc for pluginification
o services.inc includes unbound.inc rightfully, a bit like a
  plugin would do in the future, but this also means we can
  zap all requires from top pages, which are entirely spurious.
o get_dns_servers() moves to system.inc because it is used by
  status_interfaces.php
o RIP read_hosts()