Y.Model.Vanilla on the server side instead of Y.Model

## Goal

* Provide a consistent api between models in the server and models in the client
* Provide a performance solution for models in the server considering that we don't want to support events in that runtime

## Investigation

Y.Model and Y.Model.Base seems to be consirable slower than vanilla, which uses the same API but does not rely on Y.BaseCore. The preliminary results are:

```
new Y.Model.Vanilla() x 119,220 ops/sec ±1.03% (97 runs sampled)
new Y.Model.Base() x 23,223 ops/sec ±2.95% (92 runs sampled)
new Y.Model() x 14,673 ops/sec ±2.56% (79 runs sampled)
```

> Fastest is new Y.Model.Vanilla()

These results are based on this operation:

```
(new Y.Model.Vanilla({miami: 'florida'})).toJSON();
```

which is pretty much what we do internally per mojits with `mojito-data-addon` enabled.

## Solution

* As an interim solution we will use `Y.Model.Vanilla`, which is hacked into the mojito framework until `Y.Model.Base` gets ready