Replace a time-consuming lookup for the ERD dataset

# Problem

At the moment, the ERD dataset has a time-consuming lookup operation to transform freebase IRIs to DBpedia IRIs.
See https://github.com/dice-group/gerbil/blob/master/src/main/java/org/aksw/gerbil/dataset/impl/erd/ERDDataset2.java#L100

# Solution

There are two possible solutions:
1. The easiest solution would be to run the lookup once and store the dataset with the retrieved DBpedia IRIs (e.g., as NIF file).
2. Make use of a sameAs lookup service

Start with src/main/java/org/aksw/gerbil/dataset/impl/erd/ERDDataset2.java around line 100, where the Freebase-to-DBpedia IRI lookup is described. Compare the two proposed directions—storing retrieved IRIs in a NIF file or using a sameAs lookup service—and clarify which approach is wanted. Done means the ERD dataset no longer performs the time-consuming lookup during its normal use.

Written by the indexing model from the issue text.