Validate metadata against json schema

[anne17]

We should have a json schema for validating metadata objects to ensure that everything follows the same standard.

[StaffanMelin]

The datacite python package has a validator with a json schema, maybe that can be of help?

https://github.com/inveniosoftware/datacite

[anne17]

Martin will soon provide us with a yaml schema!

[MartinHammarstedt]

The schema is finished, but we first need to complete #34 before we can use it.

[StaffanMelin]

From Martin:

i terminalen så kan du använda t.ex. https://github.com/santhosh-tekuri/boon.

kontroll i Python med biblioteket jsonschema.

[StaffanMelin]

Added arg --validate (default False).