Added initial support for arbitrary string identifiers in metacat (referred to as a guid). The new identifier table is used to map arbitrary string identifiers to Metacat's current docid format (referred to as the localId). Added a new IdentifierManager class to manage this table, adding new mappings as objects are added to the system. Modified the MetacatTest service to utilize this mapping table to look up a localId from a guid. IdentiferManagerTest is working with these guids now, as is the MetacatTest service get() method, but other parts of the system are unaware of them (e.g., create, update, delete operations are unaware, and no mapping is created when new documents are created). As a consequence, the MetacatRestClientTest is not working (although it also had lots of hardcoded dependencies that need to be fixed as well).