Transformer: Calculate vacant lot pricing

[mrpetrocket]

One of the search criteria in our vacancy app is "by price". For properties with the appropriate information, we need to calculate price and add it to the property record. This will happen in the transformer. Calculating price involves many city rules and assumptions and is not trivial. A previous collaborator has dug into vacant property pricing and written a script which you can find in resources/price_merge.py.