Get `nextObject()` to work for lists and sets

Hacktoberfest participants wanting to practice test-driven development (TDD) in Java, here's one for you:

Currently `nextObject()` in `randomness.ExtendedRandom` only works for arrays. There are stubs for lists and sets that always return either the first object of the list or the first object given by the set's iterator.

Your pull request should have more than one commit. In the first commit, there should be no changes to `ExtendedRandom`, maybe only to `ExtendedRandomTest`.

Don't use the same `E` types that I used for the array tests. Also test that `nextObject()` called on an empty list or set throws `NoSuchElementException`.