Various types of reach ID and HRU ID in network data

[nmizukami]

Issue: currently allow only 32bit integer for river network ID.

ideal: allow 32bit, 64bit integer and string for IDs.

Possible solution: Create module to read IDs based on netCDF type and then generate dictionary (hash table) to map internal ID (which use 32bit integer) to these external IDs. use internal ID for network topology augmentation.

Plan to work on this dev1.2_hru-id branch