Prevent adding reserved collections

`Applications` type is reserved.
I think a bug. So, I fixed.

```javascript
PUT http://api.usergrid.com/realbeast/sandbox
{"metadata":{"collections":{"applications":{}}}}
```

```javascript
{
    "action": "put",
    "application": "886da02e-eb67-11e1-a48b-12313b123089",
    "params": {},
    "uri": "http://api.usergrid.com/realbeast/sandbox",
    "entities": [
        {
            "uuid": "886da02e-eb67-11e1-a48b-12313b123089",
            "type": "application",
            "name": "realbeast/sandbox",
            "created": 1345536570104,
            "modified": 1363159840035,
            "metadata": {
                "collections": [
                    "activities",
                    "applications",
                    "asdfasdfs",
                    "assets",
                    "devices",
                    "events",
                    "folders",
                    "groups",
                    "roles",
                    "tests",
                    "users"
                ]
            },
            "registration_requires_email_confirmation": true
        }
    ],
    "timestamp": 1363159840019,
    "duration": 31,
    "organization": "realbeast",
    "applicationName": "sandbox"
}
```