adding a cron job to refresh vocabularies

[menzowindhouwer]

Adding a crontab and a job to run entrypoint.py (see https://code.huc.knaw.nl/tsd/docker-backup for adding a cronjob)

entrypoint.py inspects the refresh setting of each vocab yml. If the time since last mofification has passed the vocab needs to be refreshed.

The last modification can be stored in the GraphDB:

<named Graph URI> <http://purl.org/dc/terms/modified> "<epoch>" 

this property can be updates using SPARQL UPDATE or you can have many where the maximum one is the most current.