Enhancement: Further validations for gbfs.json

[hbruch]

Currently, the gbfs.json file is checked for schema compliance.

In addition to this, I suggest to add the following checks:

• gbfs.json MUST contain one feed with name system_information (spec says it is system_information is REQUIRED)
• gbfs.json MUST contain at least one of feed of station_information or vehicle_status. Both files are conditionally required for either dock/dockless systems.
• IF gbfs.json declares a station_information feed, it MUST also declare a station_status feed

[testower]

This should be in the json schema