SchemaLoader.loaded event

**Description**
`SchemaLoader` should raise an event when a new model definition is being added to the collection.

**Solution**
Use `@themost/events#SyncSeriesEventEmitter ` and emit `SchemaLoader.loaded` to any subscriber e.g.

```javascript

constructor() {
    this.loaded = new SyncSeriesEventEmitter();
}

setModelDefinition(model) {
 //...
 this.loaded.emit(model);
}
```