NetQASM interfaces for QNE/QNOS integration

[cmvanb]

Interfaces for NetQASM programs intended to run in multiple environments (e.g. SquidASM and QNodeOS) with identical code.

[bvdvecht]

Hi Casper, thanks for your PR!

The interface seems simple enough and therefore I see no issues with it.

I do have some more general questions regarding the intention of this interface:

• How does this relate to the Application class in netqasm.runtime.application?
• How will programs be instantiated and executed? Will this also be defined in this interface in the future?
• Is the intention to port current application source code in this repository to use this new interface?
• Is the interface intended to be used only with the "multithreading" variant of SquidASM? The "stack" variant requires the programmer to put yield keywords in the source code, which makes the application code not be exactly the same as one would write for say, QNodeOS.

Looking forward to hear your thoughts.