We no longer use DebuggerConnection to manage the DebuggerWindowController, but now...

We no longer use DebuggerConnection to manage the DebuggerWindowController, but now it's vice versa

Benefits:
- There was a problem that when we quit we would crash, because on window closing, the WindowController would tell the connection to shutdown, but because AppDelegate cleaned up before the WindowController, it would crash when sending the message.
- An array of connections no longer needs to be managed because the WindowController stores all the pointers, so when it closes things are deallocated properly