F merge entities

A function to merge entities, which is needed by different modules, e.g. the crawler 2.0.

There are some functions dependent on this MR, e.g. !45 (merged) . If possible, review should be done simultaneously.

There is a basic unit test.

src/caosdb/apiutils.py

@@ -727,14 +727,14 @@ def merge_entities(entity_a: Entity, entity_b: Entity):
     for key in diff_r2["properties"]:
         if key in diff_r1["properties"]:
             if ("importance" in diff_r1["properties"][key] and
-                "importance" in diff_r2["properties"][key]):
+                    "importance" in diff_r2["properties"][key]):
                 if (diff_r1["properties"][key]["importance"] !=
-                    diff_r2["properties"][key]["importance"]):
+                        diff_r2["properties"][key]["importance"]):
                     raise NotImplementedError()
             elif ("importance" in diff_r1["properties"][key] or
                   "importance" in diff_r2["properties"][key]):
                 raise NotImplementedError()
-            
+
             for attribute in ("datatype", "unit", "value"):
                 if diff_r1["properties"][key][attribute] is None:
                     setattr(entity_a.get_property(key), attribute,