Way less globals

Lets see if the commit comments appear here
This does not solve the dependencies issue.

I think we need this api for the manhole:

- __init__ - keep configuration, no side effects
- install - patching fork, register signal handlers
- activate - bind socket, start thread

In oneshot mode, the mahole is installed but never activated
in activate_on mode, the manhole is installed but activate only when receiving the activation signal
in default mode, the manhole is installed and activated immediately

So when manhole thread run,  _MANHOLE.get_socket() is available.