lehreronline_spider v0.0.7 and slightly reduced es_connector log-spam

[Criamos]

This PR includes

• lehreronline_spider v0.0.7
  • metadata-changes (suggestions made by Romy)
  • refactoring
  • crawler performance improvements (massively reducing the amount of HTTP-Requests made by Scrapy)
  • in order to make these changes, methods like getId, getHash and hasChanged needed to be re-implemented for this crawler
• es_connector: slightly tuned down logging verbosity for one specific 404-response from the edu-sharing repository