Debugger: Implement listener hooks in ConnectionConfigWindow.

ConnectionConfigWindow:
- When notified that settings have been changed by the current config view,
validate them, and if complete, enable the connect button.
- Implement message handler for connect button.

Debugger: Implement use of connection config roster.

Debugger:
- Initialize/Deinitialize roster as appropriate.

ConnectionConfigWindow:
- Implement config view listener interface, and use roster
to retrieve and add appropriate config view when switching
between interface types.

Debugger: Add connection configuration window.

ConnectionConfigWindow:
- Utility window that is spawned in response to requests to create a new
remote host connection. Allows setting up and attempting to make a
connection.