Refactor select gens to ask/tell and add wrapper (experimental)

[shuds13]

Refactored:

• gpCAM gen

[jlnav]

experimental/class_gens_ask_tell's Generator superclass also has initial_send and final_tell methods which may simplify some logic.

We'll also need to find some compromise on how these classes should be initialized. We've both taken different approaches.

[shuds13]

Now in #1307