Adding synaptic parameters

[christian-oreilly]

We need to add a sufficient set of synaptic parameters to the dictionary. Also, we need to better manage the relationship between the concept of required tags and the concept of relationship. There are currently no means to specify in the required tags that these parameters need the specification of two cell types, and what is the relationship between these two required cell types (i.e., pre versus postsynaptic).

[christian-oreilly]

To start at least adding the parameters to the modeling parameters control vocabulary, we used the || notation in the required tag as follow:
{"property(from)||sao1813327414":"Cell", "property(to)||sao1813327414":"Cell"}
The following related issues still need to be addressed:

1. The use of a dictionary using id:label for required tag does not support having multiple instance of a given id. We should start to replace every use of such dictionaries by list (or similar containers) of Tag and RequiredTag objects.
2. These required tags need to be "linked" or integrated with the use of the Relationship objects (both in Nat and NeuroCurator).