Fix neighbors/outgoing/ingoing with weights=False

[janezd]

Issue

Methods that return neighbours or ingoing or outgoing connections fail if weights=True. This code was obviously never used and never tested.

Network widgets are in dire need of unit tests. :(

Description of changes

A fix would be to add a pair of parentheses (vstack expects a tuple, not multiple arguments).

However, node indices are ints and weights are floats, so we should put them into the same array. Instead, the function now returns a tuple. Since nobody could have used the code, we need not care about backward compatibility.

Includes

• Code changes
• Tests
• Documentation