Add the ability to block undelegated DNS zones

Using the generic pattern matcher as a first iteration, but we can
save some memory and CPU cycles by building and using a critbit tree
directly.

dnscrypt-proxy/plugins.go

@@ -118,6 +118,9 @@ func (proxy *Proxy) InitPluginsGlobals() error {
 	if proxy.pluginBlockUnqualified {
 		*queryPlugins = append(*queryPlugins, Plugin(new(PluginBlockUnqualified)))
 	}
+	if proxy.pluginBlockUndelegated {
+		*queryPlugins = append(*queryPlugins, Plugin(new(PluginBlockUndelegated)))
+	}
 
 	responsePlugins := &[]Plugin{}
 	if len(proxy.nxLogFile) != 0 {