Adapted language reporting tools from VUFIND-149 as part of module.

Flashmessages view helper no longer relies on FlashMessenger object attached to the view -- instead it uses dependency injection through the plugin manager.

Added missing property comment; suppress PHPMD warnings about children (ILS driver base class is expected to have many children).

(best we can do until this issue is resolved: https://github.com/sebastianbergmann/phpcpd/issues/10)

For better performance, delete comment element from page rather than reloading entire list via AJAX after removing a comment.
One small disadvantage: the "Be the first to leave a comment!" message no longer appears if the last comment is deleted; this seems like a reasonable price for better performance.

Style fixes.