AbstractLocusIterator uses a ArrayList but uses it like a queue

[yfarjoun]

The accumulator field is used with the following access patterns:

• .remove(0)
• .add(element)
• .add(0)
• .sublist(0,i).clear()
• .get(0)
• .get(i)

as one can see, except for the last item, these would all be better implemented using a Deque, but the random access isn't supported by a deque. I think it would be good to profile performance and observe how much compute is used in the accumulator .remove(0) and .add(0) calls, and if it's not insignificant, implement a Deque that has random access and use it.