Make Axis.by() generate a list of named groups instead of anonymous groups

[alixdamman]

@gdementen good idea or bad idea?

[gdementen]

As I explained orally, I don't think this is necessary (when the groups are used, their str() representation is used which is good enough I think). Besides, in the future, .by() should create a Grid I think. I know you still haven't seen that object but a "preliminary" version of this will be coming "soon" so that you can at least see what this is all about even though it is not ready yet.

[alixdamman]

Closed because not necessary

[gdementen]

After thinking about it... Maybe it would be a good idea to do it (even though it is not strictly necessary) to make things more obvious. After all, the "zen of python" states "explicit is better than implicit" (and it does not cost us anything anyway).