change IModel to readonly by default

I have removed setObject() from IModel and moved it to IWriteableModel. This time i tried to make as less impact as possible. All test are green (you hat to disable the clirr plugin because of api changes to 6.0.0).

Why?

You can not say if a model is read only by its type. You can not force a component not to change your model value (based on the type of the model).

I would like to change this. This is a first step to show, that it is possible.