Molecule Bead
=======================
Arguments:

  * `nmolecule` (int) - Number of molecules in simulation
  * `moleculeX` (json object) - Information about `moleculeX` where `X` ranges from 0 to `nmolecule-1`. In each `moleculeX` object the following must be specified:

    * `type` (string) - Type of molecule. Here `PolymerBead`
    * `label` (string) - label for this molecule, defaults to `molX` 
    * `bead_species` (string) -  Species type of bead
    * `volume_frac` (float) - Volume fraction of `moleculeX` in the simulation. Must be 0-1.
    * `ncopies` (float) - number of copies of `moleculeX` in the simulation. Note that either `volume_frac` or `ncopies` can be specified, not both. 
      

Example (python)::

  fts.add_molecule(type='Bead',bead_species='A',volume_frac=0.5)

Example (json)::

     "molecule0": {
       "bead_species": "A",
       "type": "Bead",
       "volume_frac": 0.5
     },


Check out Nb#5p32-33 for notes on this molecule