Quantum Control Stack object and program flow

The Quantum Control Stack object should serve as a hardware agnostic interface to communicate with different hardware backends.

Where the compilation of a schedule should allow us to specify what we want to do in a program, the control stack is responsible for executing this.

The control stack should support commands similar to:

• upload_program()
• start()
• stop()
• retrieve_values()

It needs to hide all the hardware-specific differences and complexity of synchronizing and communicating between modules behind an interface that can accept the compiled programs.

@dcrielaard has a prototype for this. Feel free to add some images or other materials here to initiate the discussion.

This issue was spawned from discussions in #36 (closed) .