XMI Import/export includes references

[Erik]

It would be nice if, while doing an xmi import or export (also available through baselines), that referenced artefacts from outside the package being imported are considered.

We have a growing model where we reuse existing elements from other "packages of the model". When we baseline, those elements that are used within the baselined package are not considered. This leaves us with the problematic of baselining the entire model, which takes a long time.