Add internal call that returns the endorsing node/entity of the ROFL app instance

[kostko]

There should be internal calls (e.g. rofl.AuthorizedOriginNode, rofl.AuthorizedOriginEntity) that return the address of the endorsing node or its entity when the origin of the call is a ROFL app instance. The only argument should be the ROFL app identifier.

In case no entity information is available for a node, the rofl.AuthorizedOriginEntity call should fail.