Improve messages for review distribution

When using groups, it is not directly clear from the messages how reviews will be divided.

I think we should add something like:

Group makes submission -> each individual student reviews [n] submissions -> one member of each group submits an evaluation for each review received.
Student makes submission -> each student reviews [n] submissions -> each student submits an evaluation for each review received.

The display of this should be based on whether groups are present and whether review evaluations are enabled.

Multiple versions might complicate this a bit.

We should think about the best way to display something like this, ideally we make a bit of a block diagram out of this.