Rename `LineModel.connections` to `LineModel.edges`

[Makman2]

This name is more compliant with other software and also more descriptive.

[AsnelChristian]

can i work on this

[Makman2]

Because this is an API break, we have to release 3.0 as next release then 👍

[Ananthavijay]

can i work on this @Makman2

[Makman2]

We should really do this later as this breaks API (that's why it's scheduled for https://github.com/Makman2/CE3D2/milestone/4), I want to do as many issues as possible that keep the API as is.