Connect to the debugger

[jtpio]

Now that there is a minimal UI for the debugger, we could start using the DebugSession to send debug requests to the kernel and have a "loop" in place:

• start the debugger
• initialize (set config and breakpoints)
• request scopes and variables
• stop the debugger

[jtpio]

How about we add the start and stop buttons in the Debugger MainAreaWidget for now?

(while we figure out whether to automatically start the debugger or not)

[jtpio]

cc @afshin @KsavinN

[KsavinN]

What about in the sidebar and right-click menu?

[jtpio]

With the app.contextMenu? That would be fine too.

[jtpio]

I would say the idea is to have them somewhere so we can send the debug commands. And we can move them (or remove) somewhere else later on.

[jtpio]

Connecting to the debugger was added in #47.

The other points have their own issues (#43 and #44), so we can close this one.