Added columns to csv output: node_id and node xyz
Updated merge_synapse_ids() for new CSV columns.
Debugged merge_synapse_ids() and moved it to its own file so it can be called from the command line.
merge_synapse_ids: Output row uses the minimum distance entry from its merged inputs.
Renamed "slice_count" column to "node_count"
Added columns for size and uncertainty.
merge_synapse_ids: Average coord is a weighted average.