Add per-residue properties to glmol_embed and update ResidueSpectrum.

Adding additional "per-residue" properties to glmol_embed, used by
declarative representation modifiers to generate custom representations.
Adding logic to pose_display to add residue number and residue score
terms as stored properties.

Updating ResidueSpectrum to operate on stored properties, as well as
adding ColorMap initialization logic.

Removing explict repr_entries from glmol_embed constructor, repr
modifications should be made via declarative interface.

Updating all demos to declarative repr interface.
Add object-based selector statments, update residue properties.

Adding object-based selector syntax with support for basic selection
types and subselections. Updating residue properties to lists indexed by
residue_number rather than dicts indexed by residue identifier. Updating
repr definitions to use object selectors.