Improve pre/post write decorators
- Added priority
- Handle if methods are overridden in subclasses, by mergin all defined dependencies.
Last feature is for case, when you hanve Models A with method meth_1
that has to be called when field field_1 is changed.
Next you want to add one more module, that adds new field field_2, and
want to call same method meth_1 when field_2 changed.
Next you want to add one more module (that does not know about module
2), that adds new field field_3 and want to call same emthod
meth_1 when field_3 changed.
So, no you can override same method in subclasses and specify only new
fields in pre_write or post_write decorators, and system will
automatically call same methon when any of (field_1, field_2,
field_3) changed.