JsonSchemaContent: Minor clean up

Authored by Krinkle.


JsonSchemaContent: Minor clean up

  • Double line break.
  • Allow subclasses to change $modelId. EventLogging depends on MediaWiki's JsonSchema to be extendable, seems fair for it to allow extension as well.
  • Make methods explicitly 'public' to match the parent class.
  • Minor documentation tweaks.
  • Follows-up I335ad42bb8: Simplfy objectRow even further by special casing one key and calling the parent otherwise.
  • Fix "PHP Notice: Undefined offset: 1" followed by "PHP Fatal error: Call to a member function getTitle() on null" in objectRow. Trigger when user input for a '$ref' property does not contain a slash.

Change-Id: I8910872fea84eebb3455797dbddcdeb1d9034997