Add biological entities to PyOpenWorm to support parameter changes for aging

[slarson]

This is for the PyOpenWorm repository

• ventral nerve cord
• motor neurons
• muscles cells
  • muscle receptors (for amplitude of PSCs)
  • excitatory nicotinic acetylcholine receptors (nAChRs)
  • inhibitory GABA receptors
• neuromuscular junctions (NMJs) in the ventral nerve cord
• Pre-synaptic motor neurons
• neurotransmitters
• muscle receptor channels
• post-synaptic currents (PSCs)
  • amplitude and frequency of PSCs
• synaptic vesicles
  • neurotransmitter uploading to synaptic vesicles
  • quantal size
    • the amount of neurotransmitter released from synaptic vesicles
  • vesicle docking/priming
    • the size of the readily releasable pool (RRP)
  • vesicle fusion

[slarson]

moved: https://github.com/openworm/PyOpenWorm/issues/6