remote_allow_ranges: allow inside CIDR specific remote_allow_lists (#540)

This allows you to configure remote allow lists specific to different
subnets of the inside CIDR. Example:

    remote_allow_ranges:
      10.42.42.0/24:
        192.168.0.0/16: true

This would only allow hosts with a VPN IP in the 10.42.42.0/24 range to
have private IPs (and thus don't connect over public IPs).

The PR also refactors AllowList into RemoteAllowList and LocalAllowList to make it clearer which methods are allowed on which allow list.

hostmap.go

@@ -622,7 +622,7 @@ func (i *HostInfo) Probes() []*Probe {
 
 // Utility functions
 
-func localIps(l *logrus.Logger, allowList *AllowList) *[]net.IP {
+func localIps(l *logrus.Logger, allowList *LocalAllowList) *[]net.IP {
 	//FIXME: This function is pretty garbage
 	var ips []net.IP
 	ifaces, _ := net.Interfaces()