Report ReferenceSchema Event only when it match the schema

[afranzi]

This PR aims to report the ReferecenceSchema event only when the schema is matching against the event.

[coveralls]

Coverage remained the same at 90.597% when pulling 526ea84 on afranzi:reference-schema into 6ed56f9 on everit-org:master.

[erosb]

Hi! This change can break existing behaviour (so it can break other users' visitors), can't it?

[afranzi]

Yes, this change can break existing behaviour :(

The issue, is that json-schema is reporting the schema referenced even if the schema is not maching. Should we move to use the same approach of Match/UnMatch event with the Referent event?

So we can inform in the Listener if the Referenced Schema is matching or not?