Break dependencies of the model

The model acquired many global dependencies over time. For example Exception::showException(). This is then used to be "better safe not sorry" mode in some code which makes it hard to break dependencies(it is even not clean what exception should be handled). I think the code should document which exception should be handled.

I can only think about the rewriter exception and I think the code should describe that. With the new validation code we can remove most of the other exceptions and hopefully make it more clear.

You can use different compile settings but that is complicating the build system and makes testing harder. There are different ways to fix it. Sometime a global variable(callback) is working but that has drawbacks too. Better are interfaces but that would result in large refactorings. So we should be pragmatical and use what works and clean it up over time.