Adding object twice

[romaninsh]

When an object is already added into the container, adding it again may cause some problems (e.g. maybe same ID, or project needs additional initialization).

One scenario would be if you create field object, add to one form then add to another one, what should happen? Or if you take field from one model and add it into another?

History

Initially, this was permitted and init() would be called again when added the second time.

In #41 we added protection preventing from second initialization, but it created some problems.

In #48 we changed so that init() is not called the second time.

Ideas

When adding the existing object into another container, call attach() method.

[romaninsh]

addressed in #48