Implement JSON archive filename parsing

For the JSON archive importer I have written the code to parse the
filenames and split them up. Apparently, I will be required to take
the harvesting date from the filename itself. Also I have added the
archives directory to gitignore.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>
Add import POST command

I have renamed the import route to importer so I could add a POST route
for the path import. This POST command should be used to trigger the
import of the repositories into the database. For now it will be based
on the default YAML file which is also used in the Metadata Harvester.

Signed-off-by: Konrad Reiche <konrad.reiche@gmail.com>