rpc: Move contents of __init__.py to new commands.py, connection.py files

[m-yac]

This mirrors the organization of the SAW python bindings, and will enable us to export a new interface from __init__.py which depends on the old. The exports of __init__.py should stay the same, so no scripts should have to be updated.

[pnwamk]

I would add those two names to __all__ for consistency and then I think this is good if everything works unmodified (which it looks like it does).

[atomb]

Looks good to me, too. (I'm assuming that the large removal and addition chunks are just to move code, rather than change it, so I haven't looked at them carefully.)