Improve Bindings

[skaldarnar]

• add a simple way to create ReadOnlyBinding<T> from a Binding<T>. Where to add helper methods like this?

  public static <T> ReadOnlyBinding<T> fromBinding(Binding<T> binding) {
    return new ReadOnlyBinding<T>() {
      private final Binding<T> internal = binding;
  
      @Override
      public T get() {
        return internal.get();
      }
    };
  }

• ensure that most properties are also exposed as read-only bindings; double check set binding vs bind

• document which accessors should be available for bindable properties