hafas-client@6

[derhuerst]

• [ ] consider using package entrypoints – too brittle with p/*
• [ ] wait for https://github.com/aneilbaboo/replayer/issues/28 to be resolved – using Polly.js now
• [x] remove DEBUG=hafas-client in favour of a better logging mechanism
• [ ] parseLine -> parse{Product,Line}? moved to #275, postponed to hafas-client@7
• [x] get the integration tests working again (fixtures currently don't work somehow)