Realm Management error feedback when creating triggers with invalid URLs

[Pavinati]

When installing a trigger with an invalid URL, Realm Management should return an error message specifying why the entity is not valid. Same as other fields in the Trigger.
eg:

{"errors":{"name":["can't be blank"]}}

Action:
installing a trigger with an invalid http_url

Expected result:

{"errors":{"http_url":["is not a valid URL"]}}

Actual result:

{"errors":{}}

[Annopaolo]

Closed by #750.