Saving track configs in stateful URL.

Tracks in JBrowse view are saved/loaded in/from URL.

Behavior is enabled by default in JBrowse app. However, in order to turn it on in other apps (GenCover), JBrowse directive needs **keepState: true flag**. 

 
Issue here is that config is intended to be:
```js
config = {
   someGenialisType: {
   },
   someGenialisType: {
   }
}
```
so that addTrack automatically extends the configuration with the correct one.
GenialisTypes should be fixed and unique per each track (because dataType isn't)

It should make configuration easyer, I hope ([gencover config example](https://github.com/genialis/genapp-gencover/blob/develop/static/genapp-gencover/app/controllers.report.js#L316))