Added `Config.get_device_id()` classmethod.

platypush/config/__init__.py

@@ -581,6 +581,15 @@ class Config:
         assert workdir
         return workdir  # type: ignore
 
+    @classmethod
+    def get_device_id(cls) -> str:
+        """
+        :return: The configured/default device ID.
+        """
+        device_id = cls._get_instance().get('device_id')
+        assert device_id
+        return device_id  # type: ignore
+
     @classmethod
     def get_cachedir(cls) -> str:
         """