Cleanup oneway and railway=spur/siding in SQL

- The tag railway=spur/siding is no longer rendered. Please use highway=rail,
  service=spur/siding instead. This resolves #367.
- Rationalise oneway scoping in queries. This resolves #368.
Merge pull request #409 from math1985/sql-oneway-ssy

Cleanup oneway and railway=spur/siding in SQL