Add backwards compatibility for old DatasetID's

[kmdouglass]

Here's what happens when you try to open an old Datastore (1.0.1 and below) with the current 1.1.1:

myDB = db.HDFDatastore(Path('./datastore.h5'))

Unexpected error when loading the Datastore's persistent state: <class 'TypeError'>

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-4-e26258ed339c> in <module>()
      1 # Specify the database
----> 2 myDB = db.HDFDatastore(Path('./datastore.h5'))

/home/douglass/src/bstore/bstore/database.py in __init__(self, dsName, widefieldPixelSize)
    259 
    260         # Read the persistence data from the HDF file
--> 261         self._loads()
    262 
    263         # Lock file to prevent concurrent writes

/home/douglass/src/bstore/bstore/database.py in _loads(self)
    728             with h5py.File(str(self._dsName), mode='r') as file:
    729                 serialObject = file[self._persistenceKey]
--> 730                 objFromHDF = pickle.loads(serialObject.value)
    731                 self.__dict__.update(objFromHDF.__dict__)
    732         except OSError:

TypeError: __new__() missing 1 required positional argument: 'replicateID'

[kmdouglass]

It's likely that no one will ever use 1.0.1, so I'm closing this with a Won't Fix label.