ResidueSelector.selected_atoms and ResidueSelector.selected_residues regression

[avirshup]

Regression after merging the no-RPC stuff. After making a selection:

`rs = mdt.widgets.ResidueSelector(mol) rs``

Expected: Before the merge, rs.selected_atoms would yield a list of atoms, and rs.selected_residues would yield a list of residues:

>>> rs.selected_atoms
[<Atom HO5' (elem H), index 0 (res DA50 chain 1) ... >,
 <Atom O5' (elem O), index 1 (res DA50 chain 1) in ...>, ...
]
>>> rs.selected_residues
[<Residue DA50 (index 0, chain 1) in Molecule: Unnamed molecule from OpenMM>]

Getting: rs.selected_residues returning a list of strings; rs.selected_atoms doesn't appear to be working.

>>> rs.selected_atoms
AttributeError: selected_atoms
>>> rs.selected_residues
['DA50']

[justinmc]

Fixed over here: https://github.com/Autodesk/molecular-design-toolkit/pull/106