Unique asset names for links references

Today, when we transform an ABS model into JSON, the links use the index corresponding to the asset's position in its group as a reference to it (sourceAsset, targetAsset). We need to do away with these index-based references, so that we can update parts of models without having to recalculate all the indexes, and thus update the models as a whole. The solution we're aiming for is to make the asset name unique, so that it can be used as a reference.