Add directory check for the logger instantiation

Since the configured directory might not be present this commit adds a
check whether the path exists and creates it if it does not exist. This
will fail if the user starting the CKAN process does not have sufficient
rights.

Signed-off-by: Konrad Reiche <konrad.reiche@fokus.fraunhofer.de>
Write unit test for Moers Harvester

To test the functionality of the new harvester I have added a small unit
test which is based on a sample dataset of the Moers JSON dump. With
this I found some small mistakes which are fixed by this commit as well.

Signed-off-by: Konrad Reiche <konrad.reiche@fokus.fraunhofer.de>
Activate Moers Harvester plugin

One thing the implementation was missing is the generation of the unique
identifier since the datasets do not come with a predefined identifier.
It is generated the same way as in the other JSON dump harvester.

There is still a problem with the unicode characters in the name, I was
not able to replace them with their ASCII counterparts (ae, oe, ue, ss)
without decoding exception. This will be fixes as soon as possible.

Signed-off-by: Konrad Reiche <konrad.reiche@fokus.fraunhofer.de>