Add loadMolecule() RPC method

This adds a new RPC method to load a molecule given a data file
and a format. This replaces the existing loadFromChemicalJson()
method.

Change-Id: Id031feebb1197f2b3327c06d6605db539b0c7eab
Merge topic 'rpc-load-molecule' into master

9aa69af3 Add loadMolecule() RPC method