Integrated publisher policy into build

- Publisher policy creation can now be done via the csproj,
  with the PublisherPolicy target
- Deleted old batch file method
- Integrated new method into Npgsql, Npgsql.EntityFramework and
  Npgsql.EntityFrameworkLegacy
- Updated version numbers

Note: we still have to manually manage bumping the versions,
need to find a proper solution for this