Inherit from AutoWatcher to make 'this' a proxy object that
watches for its own property changes and calls the method given
(takes a string because 'this' is unavailable when calling 'super').
This can be used to e.g. automatically call a rendering function
if a property is changed.
Using inheritance is necessary because 'this' is immutable,
and isn't defined in the class constructor _unless_ super() is called.
(thus you can't do something like this = new Proxy(this) at the end).