No extension parameter support available

[dotasek]

The -extension option isn't available for the online validator:

https://confluence.hl7.org/pages/viewpage.action?pageId=35718580#UsingtheFHIRValidator-Extensions

The UI should occupy its own section of the options page, like IG selection does, and :

1. The any magic word should be its own checkbox widget, probably with text like allow all unknown extensions
2. An interface similar to our IG widget allowing multiple entries. Instead of a dropdown selection though, it would need to be a text field.

[dotasek]

I believe that the following simple Patient resource should fail if there are no extensions specified:

{
    "resourceType": "Patient",
    "extension": [
        {
            "extension": [
                {
                    "url": "ombCategory",
                    "valueCoding": {
                        "system": "http://terminology.hl7.org/CodeSystem/v3-NullFlavor",
                        "code": "UNK",
                        "display": "unknown"
                    }
                },
                {
                    "url": "text",
                    "valueString": "unknown"
                }
            ],
            "url": "http://hl7.org/fhir/us/core/StructureDefinition/us-core-race"
        }
    ]
}