Add @api decorator

CURA-6665

cura/Utils/Decorators.py

@@ -0,0 +1,19 @@
+# Copyright (c) 2019 Ultimaker B.V.
+# Cura is released under the terms of the LGPLv3 or higher.
+
+import functools
+
+
+##  Decorator for functions that belong to a set of APIs. For now, this should only be used for officially supported
+#   APIs, meaning that those APIs should be versioned and maintained.
+#
+#   \param since The earliest version since when this API becomes supported. This means that since this version, this
+#                API function is supposed to behave the same. This parameter is not used. It's just a documentation.
+#
+def api(since = "Unknown"):
+    def api_decorator(function):
+        @functools.wraps(function)
+        def api_wrapper(*args, **kwargs):
+            return function(*args, **kwargs)
+        return api_wrapper
+    return api_decorator