OAI-38: Added level to useContext

[dborowiecki]

Change required by AI module which use ServLevel as one of evaluation parameters. New entry is added to current use context for both Medication and ActivityDefinition.
New values have format:

• For Activity Definition

    {
        "code": {
            "code": "useContextLevel"
        },
        "valueCodeableConcept": {
            "coding": [
                {
                    "code": "S",  //ServLevel value 
                    "display": "Simple Service"  // Simple Service, Visit, Day of stay, Hospital case
                 }
            ],
            "text": "Service Level"
        }
    }

• For Medication

    {
        "url": "useContextLevel",
        "valueUsageContext": {
            "code": {
                "code": "level"
            },
            "valueCodeableConcept": {
                "coding": [
                    {
                        "code": "M", // Fixed value
                        "display": "Medication"
                    }
                ],
                "text": "Item Level"
            }
        }
    }