GUI: Add inhibitory cells to "Cell parameters" GUI element

[asoplata]

Problem:
Currently, in the "Network > Cell parameters" vbox, the only celltypes shown are the excitatory celltypes. However, the "Synapses" "Properties" list displays GABA synaptic parameters as well. This implies that the "Cell type" selection is actually for all celltypes within an individual layer. Contradicting this, the "Geometry" and "Biophysics" property lists do not make clear which, if any, properties belong to the excitatory vs. inhibitory celltypes of the layer. In the case that only the Pyramidal cells' Geometry or Biophysics are shown, then that means there is no current way to inspect or change the same properties of the inhibitory celltypes in the GUI.

Solution:
Add full celltype information for the L2_basket and L5_basket celltypes in this vbox. This will include splitting the "Synapses" property list.