Update river network with node ID's
•RivEX can create and populate the node fields required by the stream ordering algorithms.
•RivEX does not overwrite any existing node fields; it will always create new fields named FnodeX and TnodeX where X is an incremental number. This is done in case other data references the old ID numbers.
•Once the nodes are identified, RivEX will build topological dictionaries. These hold the network logic and are read by RivEX when building stream order or site linking.