Expose JSON-RPC methods for blobs

[mycognosist]

Thinking a bit about how to get and set blobs...

Perhaps a getter method could take the blob reference and a filepath as parameters; check for the blob in the store and write it to the given filepath. The return value is either success or an error.

Then a setter method would do the opposite: add the file at the given filepath to the blob store and return the blob reference or an error.