hypothesisConfig needs to handle JSON strings correctly

We have a new requirement for requestConfigFrameFrom var to now take an object rather than just an origin string. This is due to the fact we need to send both an origin and an numerical level index to tell the client where the LMS's via iframe resides. (e.g. levels deep)

Currently, the original via handles the json string correctly

```
window.hypothesisConfig = function() {
requestConfigFromFrame: {
origin: http://localhost:8001
ancestorIndex: 1
},
...
}
```

But via3 does not

```
window.hypothesisConfig = function() {
requestConfigFromFrame: `{"origin"http://localhost:8001","ancestorIndex":1}`
},
...
}
```

These params are sent to Via as:

* `via.config_frame_ancestor_level`
* `via.request_config_from_frame`

via3 needs to be able to take a JSON string and parse it to the template