use table to reference TAZs by arbitrary ID

[colinsheppard]

We should create a global "table" which is Netlogo's word for a hashtable/hash/dictionary to allow lookup of TAZ agents by any arbitrary integer that don't need to be ordered or start at 1.

See email I sent to you with subject "Table Benchmark" for an example of how to do this.

During setup-tazs, you'll want to add the tazs to the table as they are assigned their id from the charger input file. You'll need to remove the constraint in this procedure that requires sequential ordering of tazs in the charger file.

Finally, all locations in the code where we refer to a TAZ by number (e.g. "taz #") needs to be changed to use the table instead.

Discussion of dealing with "external" TAZs will be in another issue.