Create an Operation to add a Group to a Schema

[GCHQDev404]

Create a new Operation to add a group to a schema; together with handlers for AccumuloStore and Mapstore.

"Assuming the vertex type is consistent this should be simple as there is no existing data to break"

[GCHQDev404]

No longer within the realm of FedStore but better suited to individual store implementations.

[n3101]

@GCHQDev404 "but better suited to individual store implementations."

So should there be separate issues to:

1. add a group to a schema used by an accumulo store
2. add a group to a schema used by a map store. ??

[GCHQDev404]

@GCHQDev404 "but better suited to individual store implementations."

So should there be separate issues to:

1. add a group to a schema used by an accumulo store
2. add a group to a schema used by a map store. ??

It will be adding handlers to each store to support the operation.