NethVoice: default phone template disappear if is not used

[andrea-marchionni]

If I create a custom template for a phone model and assign it to all phones of that model, the original base model— from which the custom template was created—disappears from the list of available models.

Steps to Reproduce:

1. Add a phone using its MAC address.
2. Assign the phone to a user.
3. Create a custom template for the phone model.
4. Change the phone’s model.
5. The original base model no longer appears in the list on the model page.

[Stell0]

The problem is that when the original model scope is modified isn't shown as a scope to copy from for creating a derived one.

This is because the API used to populate the list is tancredi/models?filter[used], that show only scope used by a device. Without filter, all available scopes would be shown.
Consequence is that we can't show a model if it doesn't have a phone associated with it.
But it's ok, because it makes no sense to modify a scope that isn't used by any phone.
To have the original scope in that list, you can just add a phone, assign the parent scope model to it then you can modify it.