Use JSON for datastate serialization #43
Description
Switch from using pickle to serialize objects in datastates to using JSON.
The issue with serializing objects directly is that there are no guarantees for compatibility with future versions of the objects. Using JSON and a compatibility version tag can ensure backwards compatibility with future releases.
Requires toJSON and fromJSON methods for all structure objects in dtocean-core and some method to handle versions - maybe an attribute with the latest version and an input to specify particular versions for fromJSON.