2755 Add ability to extend HostNode, NetworkNode, Service and Application outside PrimAITE.

src/primaite/simulator/system/applications/application.py

@@ -41,10 +41,10 @@ class Application(IOSoftware):
     install_countdown: Optional[int] = None
     "The countdown to the end of the installation process. None if not currently installing"
 
-    _application_registry: ClassVar[Dict[str, Type["Application"]]] = {}
+    _registry: ClassVar[Dict[str, Type["Application"]]] = {}
     """Registry of application types. Automatically populated when subclasses are defined."""
 
-    def __init_subclass__(cls, identifier: str, **kwargs: Any) -> None:
+    def __init_subclass__(cls, identifier: str = 'default', **kwargs: Any) -> None:
         """
         Register an application type.
 
@@ -52,10 +52,12 @@ class Application(IOSoftware):
         :type identifier: str
         :raises ValueError: When attempting to register an application with a name that is already allocated.
         """
+        if identifier == 'default':
+            return
         super().__init_subclass__(**kwargs)
-        if identifier in cls._application_registry:
+        if identifier in cls._registry:
             raise ValueError(f"Tried to define new application {identifier}, but this name is already reserved.")
-        cls._application_registry[identifier] = cls
+        cls._registry[identifier] = cls
 
     def __init__(self, **kwargs):
         super().__init__(**kwargs)