add build status to README
[#79822152] Add accessed_at field to reference
set additionalProperties: false for all levels of the JSON schema except bibliographic
Merge pull request #13 from ploslabs/feature/accessed_at_field

[#79822152] Add accessed_at field to reference
Merge remote-tracking branch 'origin/master' into feature/add_reference_literal

Conflicts:
	app/models/reference.rb
	db/schema.rb
	schemas/base.json