Implementing pending SONATA `connection-overrides` properties from PR #58

[darshanmandge]

The SONATA spec defines these additional override properties that aren't implemented here:

• spont_minis: Spontaneous event trigger rate
• synapse_configure: HOC code snippet for synapse configuration
• modoverride: Synapse helper files
• neuromodulation_dtc, neuromodulation_strength: For neuromodulatory projections

Do you plan to implement these in future PRs? Should we add TODO comments ?

Originally posted by @darshanmandge in #58 (comment)