improve output (less verbose and better readable)

The current output is

```

{"name":"sphere-category-sync-0.2.4","hostname":"Nikolauss-MacBook-Pro.local","pid":47773,"level":30,"data":{},"project_key":"icecat-opencatalog-notebooks-1","msg":"Found match for externalId '1495' with id 'ef15d3a5-2d4d-4518-936e-c9ca10af38c6'.","time":"2015-10-13T10:12:16.174Z","v":0}
```

per category, which is too much on large imports and also not very readable on the console.

Would be nice to have nicer console output.