Debugger: Add connection config handler framework.

Debugger: Add connection config handler framework.

ConnectionConfigHandler:
- Abstract base class for the different types of connection that allows one to
  retrieve an appropriate configuration view based on the target host interface
  type. This will allow the configuration window to switch dynamically between
  network, USB, etc. without having to know the details of any of those.
  Initially only a network subclass has been implemented though.

ConnectionConfigHandlerRoster:
- Keeps track of the list of available config handlers, and handles mapping a
  request for a given interface info to the appropriate type of handler.

ConnectionConfigView:
- Abstract base class for the actual configuration views returned by the config
  handlers. This exposes a listener interface via which the view can notify
  an interested party that the configuration has been changed. Correspondingly,
  the configuration window will use this to determine if the configuration is
  complete enough to allow a connection attempt.