Selection is an Object, not an array.

Because of this we need to use map a little differently to map the ids, not the
entries.
Map selection to generate new object with new ids.
Make nucleotides and interactions clickable.

I've attached the event handlers to allow clickable nucleotides and
interactions.
Add menu for all PDBs in 2D view.
Merge pull request #12 from BGSU-RNA/feature/2d

Selection is an Object, not an array.