Replace Tuple<Long,V> with LongTuple<V>

Tuples where keys are Long are used a lot. Oftentimes like this:

Tuple<Long,Message> tuple=...;
long id=...;
Message msg=tuple.get(id);

This results in a long getting boxed into a Long, each time allocating a new Long instance.

Todo: create a new LongTuple<V> class