Recurse levels for ecoystem.

[Jesus Soto]

Adjust fetchPerspectives function to receive levels greater than 0 (levels > 0), and be able to explicitly use the variable inside a dgraph recurse operation.

[Jesus Soto]

Interface modification to implemented in https://github.com/uprtcl/js-uprtcl

export interface GetPerspectiveOptions {
  levels?: number;
  entities?: boolean;
  details?: boolean;
}