Revise sanity checks for iModel on import

If the extends of an iModel are too large the centroid of all elements is calculated. If elements are further away from the centoid than a certain maximum distance they are classified as outliers and not displayed in the imodel.

If the model just has two assemblies that are very far away from each other and have approx. the same size, the centroid is in the middle and nothing gets displayed in the iModel.

There is no warning in the iModel and the user just does not see anything. We would really appreciate a solution for such a case.