Do just one call to get all the edges for the given nodes, instead of
one call for each node.

This new call has been added as a new method to Graph and Backends.
GetNodesEdges, return the list with all edges for a list of nodes.

Batching is used to avoid hitting the max number of clauses set by ES
(is set to the default value of 512).

Like Descendants, but using edges in any direction (Descendants only
uses edges from parent to child, Neighbors uses from parent to child and
from child to parent).

The different with the Both step, is Neighbors accumulate nodes seen.
Example (pseudo-syntax):
A -> B -> C
G.V(A).Out().Out() return: C.

But:
G.V(A).Neighbors(2) return: A,B,C

The parameters allowed are the same as in Descendants.
Example:
G.V('foo').Neighbors('RelationType',Within('ownership','foobar'),2)

To improve speed and reduce backend load when using persistent backends,
a new method, GetNodesFromIDs, is implemented in Graph and Backends.
This method only uses one call (or a few in we have hundreds of nodes,
see batching) to get all nodes from the backend.

Batching is used to avoid hitting the max number of clauses set by ES
(is set to the default value of 512).