handling modifications to or deletion of network drives/biases

[rythorpe]

Here's a place to resolve our discussion started in #221 about whether or not we should create formal methods in Network for modifying or deleting drive/bias attributes that have already been created.

As @ntolley pointed out, there is a common use case for modifying properties of a drive/bias after it has been added, attached, and possibly instantiated within a Network instance particularly if the user is running hnn-core using a jupyter notebook. In our example scripts, we also demonstrate ways that users can copy and modify properties of a given Network instance in order to rerun the simulation for different results. Regardless of whether or not we decide to expand the API, we should streamline our examples so that we either promote modification of existing (or copied) Network instances or solely promote the creation of new Network instances.

[jasmainak]

duplicate of #235 ?

[rythorpe]

Sure enough, I didn't see that one.