The lists in the post model (current state and original state) referred
to the same objects, so that making changes to current state was seen as
if no change has been made. This broke mass tag - it always thought
there were no changes to post tags.
This has important side effect that matters when we check for data
changes using _orig dictionary. Previously, _orig was empty (so its
members fields were undefiend) whereas the real fields were declared as
nulls. This meant that for new entities, the conditions were always
true, which is unintended. Now both _orig and the class itself are
initially populated with _updateFromResponse which syncs the state
between them, removing the problem.
- Hide fields that are uneditable, rather than disabling them
- Support fragmented edit privileges (e.g. roles than can edit only some
aspects of tags) - up until now the client tried to send everything at
once, which resulted in errors for such cases.
