Templates stored within Polymer

[rwxayheee]

residue_chem_templates (ResidueChemTemplates) is an attribute of Polymer. The residue chem templates can be read from and written to JSON. Currently it includes a full set of available templates that has been loaded during the construction.

For each Monomer, there is also a template attribute but it is not a JSON-bound property (not exported to JSON or imported from JSON of a polymer).

Based on discussion we had today, we might want to re-evaluate whether we want and which templates to store with polymer. For templates generated during construction, this attribute serves as a useful cache. For templates that didn't match, retaining them may not be necessary.