Support IPv6 CIDR in recursive whitelist - Fix #2

- Add IPv6 loopback in default config
- Switch Apache Commons Net SubnetUtils to CIDRUtils
- Add some debug statements

build.gradle

@@ -54,9 +54,6 @@ dependencies {
     // DNS lookups
     compile 'dnsjava:dnsjava:2.1.8'
 
-    // Network utilities for recursive host check
-    compile 'commons-net:commons-net:3.5'
-
     testCompile 'junit:junit:4.12'
 }