SelectEObjectDialog does not sort elements to be selected

The SelectEObjectDialog does not sort its entries but uses the order in the model. This makes it hard to find elements to select in the dialog. Presenting the model content in an ordered way could improve usability.

The dialog is used e.g. while selecting data types or components to be instantiated in an assembly context.

As a first try, I vote for using an lexicographical ordering based on the labels.