Enhance calculated upstream and downstream references

[aschaal]

We have the hierarchy:

Input (-> System) -> Software -> Architecture -> Module Design

If an Input element has a link to Module Design element, which has a link to an Architecture element, which itself has a link to a Software element, we can calculate the reference between the Input element and the Software element automatically. This link can be shown it in Upstream References of the Software element and in Downstream References of the Input element.

This should be also reflected in the Traceability Report.