R6 private objects/methods

[wlandau]

No description provided.

[wlandau]

I'm probably going to keep most methods public because those bindings are already locked, so there is not much harm that can be done. But all the non-function members should be private.

[wlandau]

Nested R6 objects are tricky because those are data too. I think I will need active bindings for those. Otherwise the refactoring will be too much and the syntax will be too unnatural.

[wlandau]

In fact, active bindings in front of all private data objects seems like a good idea.