Create content wrapper for Resolvables

[atasak]

Resolvables are objects that can be represented by a (type, id) tuple. The content wrapper should resolve the object by its type and id, and update the id in the data object when it get's a new object as value.

Note that the resolving and updating is done in two different wrappers for the same data object:

a: {
    b: idOfB
}

The contentwrapper replacing b should resolve the data of b, but the content wrapper replacing a should update the id when b gets replaced by a content wrapper or data object. In the latter case, a new data object could be created.