Easy access for connector developers

Description

The minimal-connector is a great kick-off-project to start connector development. But the changes necessary for the connector to work properly for YOUR school are sometimes hidden between the lines.

This issue is about easing the learning curve for new connector developers, by providing them something like a minimal-connector-api and clear indications of what and where changes and coding needs to be done.

Explanation

There'll hopefully be a clean separation between configuration (backendUrl, licensePlate, source, etc), coding (implementing methods for getting items) and api (automatically indexing, sending data to the backend).

Dependencies, issues to be resolved beforehand

Not necessarily but: api#3 (closed)