Adding tests for indexOf and lastIndexOf.
Adding implementation of lastIndexOf.

Fixes bug in iterator that wouldn't allow backwards iteration from end.
Fixes bug in test of indexed add.
Adding test of indexed addAll.
Adds implementation of both addAll methods.

Fixes state not being invalidated in add.
Adds test of iterator.
Adding test of list iterator.
Fixes issue where next and previous were not correctly affected by set.
Adding test of list iterator starting at a given index.