First pass at change generation logic for missing addr:city

This is the first pass for fixing issue #3. It will detect where an addr:city tag can be added to an existing object and add the information required.

This information is not yet serialized to a .osc file but sufficient information is present within the tables to do so.

This code has not yet been tested for anything other than ways.
Clean up some unnecessary SQL
Add serialization code for changes.

This closes #3 althogh improved documentation and testing is required.