Improve ModelStorage.copy

* Allow callable in copy default
* Support dotted notation in copy default
* Use setdefault in copy
* Copy default when needed
* Do not set default state in copy
* Use callable and dotted notation in copy default

issue5576
issue7648
review72291002

account.py

@@ -37,5 +37,5 @@ class MoveLine(metaclass=PoolMeta):
             default = {}
         else:
             default = default.copy()
-        default.setdefault('dunnings')
+        default.setdefault('dunnings', None)
         return super(MoveLine, cls).copy(lines, default=default)