Add implementation of MethodsNT

A new version of the methods, [MethodsNT], has been specified and added to the master branch. Before it can be used in test case specifications, [MethodsNT] must be implemented in Zonemaster-Engine.

Create all methods specified in [MethodsNT].

[MethodsNT]: https://github.com/zonemaster/zonemaster/blob/master/docs/specifications/tests/MethodsNT.md