Add OPLS Parameters for ADOPA

[rmatsum836]

PR Summary:

ADOPA is molecule similar to that of L-DOPA (https://en.wikipedia.org/wiki/L-DOPA) (See image below).
The atom type for the carbon bonded to the amine group (opls_912) needed to be added to properly atom type the molecule.

Currently the following dihedral parameters are missing:

Missing dihedral with ids (15, 14, 39, 40) and types ['opls_465', 'opls_912', 'opls_900', 'opls_909'].
Missing dihedral with ids (15, 14, 39, 41) and types ['opls_465', 'opls_912', 'opls_900', 'opls_909'].
Missing dihedral with ids (18, 15, 14, 39) and types ['opls_466', 'opls_465', 'opls_912', 'opls_900'].
Missing dihedral with ids (19, 15, 14, 39) and types ['opls_467', 'opls_465', 'opls_912', 'opls_900'].

which corresponds to C_2-CT-NT-H and O_2-C_2-CT-NT. I need to do some further digging to find these dihedral parameters. For this reason, along with lack of unit testing for this molecule, I am opening as a draft right now.

PR Checklist

---

• Includes appropriate unit test(s)
• Appropriate docstring(s) are added/updated
• Code is (approximately) PEP8 compliant
• Issue(s) raised/addressed?

[codecov]

Codecov Report

Merging #454 (9173ce7) into master (b55b416) will not change coverage.
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[rmatsum836]

Looking at a typed system from LibParGen, the atom type for 466-465-912-900 is:

14.43480 -11.00392  -3.43088   0.00000   0.00000   0.00000

.

For 465-912-900-909, the dihedral parameters are:

-1.26775   3.02085   1.74473  -3.49782   0.00000   0.00000

There isn't an exact match for these in the gromacs bonded parameters (https://github.com/gromacs/gromacs/blob/master/share/top/oplsaa.ff/ffbonded.itp) but perhaps it's worth testing these parameters out.