Easier separation of SPDZ online/offline phase

[rw0x0]

To make it easier to benchmark the online/offline phase of the SPDZ/MASCOT protocol we should add the possibility to pre-produce required triples, random elements, etc. before doing the actual computations. Adding functions, like:
public void produceTriples(int el) {
ensureInitialized();
triples.addAll(mascot.getTriples(el));
}
to the SpdzMascotDataSupplier might be a good idea.