Add test to verify that dihedral analysis plots are labeled with the correct molecule and dihedral atom group

[cadeduckworth]

• link to new automated dihedral analysis for plots/figures once 217 is merged

[cadeduckworth]

@orbeckst

Updated To-Do

• manually verify that all of the dihedral atom groups, atom indices, and bond indices are correct for both examples from the testing resources (MDAnalysis/RDKit consistency check)