Debugger: Change user interface quit and ask user semantics

* UserInterface::SynchronouslyAskUser() is now allowed to return -1 to
  indicate that the user cannot be asked at this point for whatever
  reason. The caller needs to handle that case.
* UserInterfaceListener::UserInterfaceQuitRequested(): Add new parameter
  "quitOption" to specify what is supposed to happen. The previous
  behavior (ask user) is only one of the options. The others are to kill
  the debugged team or to resume it.

src/apps/debugger/user_interface/cli/CommandLineUserInterface.cpp

@@ -207,7 +207,7 @@ CommandLineUserInterface::SynchronouslyAskUser(const char* title,
 	const char* message, const char* choice1, const char* choice2,
 	const char* choice3)
 {
-	return 0;
+	return -1;
 }