Still some issues with mid-level group definitions

[rwest]

This commit rwest/RMG-database@aa5690a shows the groups we were working on. Emily added something to the group file, so that it'd be usable, and then we did some work editing them, but there are still some questions in there to be addressed.

We want the group definitions to be more general than their children, but more specific than their parent, and make chemical sense. If we can't achieve all three, then perhaps we should remove a level from the tree. Please could @kblondal take a look?