Testing issue (#3) and working with problematic repositories

Each commit is independent, so you can choose which ones you want.
- Resolving testing issue (https://github.com/ariadne-eu/ariadne-harvester/issues/3)
- Avoid stopping harvesting due to an error on a single resource
- Adding a property (harvestInterval) to harvest from the latest harvesting date until an interval of days. The default value is -1, implying that there is no interval.

Regards,

Octavio.