Implemented StorageIterator template class
* Replaces Edge- and PropertyIterator with single template class
* Renamed toId in EdgeId into nodeId to make generalised access possible
* EdgeId and and NodePropertyId elements can be separated into "area" and "nodeId"
** Area describes the iteration pool of a StorageIterator
** nodeId is the payload of the ID
* Modified WikiGraph example to match the class merge and resulting constructor generalization