Debugger: Rework to fully use TargetHostInterface.

Debugger: Rework to fully use TargetHostInterface.

Application objects:
- Rework and simplify to take into account that they will no longer be
  directly managing the team debugger list. Requests to start a new debugger
  are still funnelled through here however, and as such, said requests must
  now provide the appropriate target host to start with. Adjust StartTeamWindow
  and TeamsWindow accordingly.
- On global init, always create an instance of the local interface.

TargetHostInterface:
- Convert to BLooper and implement TeamDebugger's Listener interface.
  TargetHostInterfaces now directly manage their TeamDebugger instances,
  and consequently take over the equivalent duties that the main application
  previously had.
- Adjust signatures of Attach/CreateTeam to add const. Adjust
  LocalTargetHostInterface accordingly.
- Add accessor to determine if a given interface is local or not. Will be
  needed for the TeamDebugger's file manager eventually so it knows if it
  needs to request remote files if no matching local file is found.
- Add accessor to start a TeamDebugger instance, and corresponding options
  structure.

TargetHostInterfaceRoster:
- Minor adjustments to host interface initialization to take into account
  needing to start the looper.
- Add accessor for number of running team debuggers, for the main app to
  use when deciding to quit.

TeamDebugger:
- Add accessor for SettingsManager. Needed for the case of a restart request,
  as the host interfaces do not have direct access to it.

TeamsWindow:
- For now, always grab the local host interface when initializing the window.
  Once the remote interface is implemented, this will need to be adjusted, but
  the appropriate UI for creating/selecting it is needed first anyways.

With these changes, the main application is fully host-agnostic, and all
management of actual debuggers is delegated to their parent host interfaces.
There still needs to be a listener interface for the host interface and/or
roster though, so that the application can be made aware of when debuggers
quit, as this drives whether it's time to terminate the app or not.