Implementation of default form processor for muzima.

Expected JSON structure that can be processed by the default encounter processor is:
```javascript
{
    "dataSource": "10003df1-b8fa-4e7c-836f-41fd0ebd28a3",
    "discriminator": "encounter",
    "payload": {
        "person": {
            "person.uuid": "dd55e586-1691-11df-97a5-7038c432aabf"
        },
        "encounter": {
            "form.uuid": "fa6da034-0600-428c-9bdb-6834dba20c74",
            "encounterType.uuid": "8d5b2be0-c2cc-11de-8d13-0010c6dffd0f",
            "provider.uuid": "842f4bae-1692-11df-97a5-7038c432aabf",
            "location.uuid": "c0937b97-1691-11df-97a5-7038c432aabf",
            "datetime": "2012-12-19 08:05:09"
        },
        "obs": [
            {
                "uuid": "a8970a26-1350-11df-a1f1-0026b9348838",
                "type": "numeric",
                "value": 12
            },
            {
                "uuid": "a8a8bb18-1350-11df-a1f1-0026b9348838",
                "type": "numeric",
                "value": 465
            }
        ]
    }
}
```