Add more information to legend when a graph is generated from a group

Thanks for the great tool, I found that I would like a little more detail in some graphs that are generated from groups.

For me anything generated from a group was just displaying "series0' etc.... In the code there was a 'pretty' name but it wasn't being displayed. I added a little more specificity so we can identify not just the group but the server as well. But this issue may be better solved with slices/pointers in a few additional places, but i tried to keep my changes to a minimum.

All the tests seems to pass for me, should I be including additional tests?