Method createRequestGroups

We aren't trying to do anything fancy here, like some kind of artificial optimal group for performance or anything. We pretty much just try to fit as many locators as possible into a single valid request, and then move on. This method assumes the locators have already been sorted by start offset.

(List<ReadFunctionGroup<K>> functionGroups, List<KeyedModbusLocator<K>> locators,
            int maxCount)