CST_Anomaly(): Add 'memb_dim' and improve 'dim_anom' parameters

Hi @aho and @erifarov,

We talked about this in the individual user meeting, opening this issue to track it.

In summary, it would be nice to have the following features in CST_Anomaly():

• A memb_dim parameter. Right now the name of the member dimension is restricted to 'member'.
• For the dim_anom parameter to accept dim names. Currently it expects the number of the dimension.

Let me know if you need anything from me.

Victòria