Introduce namespace or group for Features

[bertleunis]

We started to use the new createFeature functionality, which we really like. We noticed though that all features are added to the root of the store. We have a setup where several libraries can add a feature to the store. The libraries are used in an app of course. When now two libraries each add a feature called "config", then one overwrites the other in the store used by the app. To prevent this problem we think it is maybe a good idea to introduce some kind of optional namespacing. A Feature would then have an optional property "group" or "namespace" or something like that.

The store structure for two features named "config" would then look something like:

{
  'lib-1':
    { config: { some: 'config' },
  'lib-2':
    { config: { some: 'config' }
}

What do others think?