Resource json-schema versioning

[andersoncardoso]

We need to versionate json-schemas, so we can handle updates without breaking existing data.
Some of the points to be taken in account:

• use a semantic versioning for the schemas. The minor version updates does no imply a new schema file, but major updates should require separate schema.
• the resource should provide a @version identifier (otherwise we consider it as the last available version)
• a migration mapping should be provided, so we can handle search through different schemas:

ver 1.0.0
{
    "ctid": "xyz",
    "descr": "abc"
}

ver 1.1.0
{
    "ctid": "xyz",
    "descrElements": {
        "descr": "abc",
        "shortDescr": "a"
    }   
}

Locator "dispatch" for query:
  v 1.0.0: "descr" => /descr
  v 1.1.0: "descr" => /descrElements/descr

So if someone searches for descr, there could be sql like:

where 
-- descr seach "dispatch"
(
    (schema_version = "1.0.0" and "/descr" = "abc")
    OR
    (schema_version = "1.1.0" and "/descrElements/descr" = "abc)
)

So for any searchable field, each schema version must maintain a "dispatch" locator for each searchable field. In this way, each schema is "responsible" for it's own query elements, and future schema don't need to know anything about that responsibility..

• for a jsonb 'contains' query we should find the current 'path' query, and create a list of different versions for the same 'path', ORing them together as describe above
• the JsonSchema class should handle this transparently.