specify label when registering array

[mdrio]

It would be useful to set the destination label when registering an array via arrays/register_dataset, and be able to retrieve the array by the above mentioned label. In other words, labels could be used as a way for naming and retrieving array by the client.

[lucalianas]

Started the update here https://github.com/lucalianas/ome_seadragon/tree/update_register_array

Let's put this in pause for the moment