Considerations for a next major version

[Haroenv]

The concept of "disjunctiveFacets" & "disjunctiveFacetsRefinements" are causing issues if you want to merge two search parameters. This is something we want to do if we are doing federated search; where refinements are kept bottom-up, unless a refinement was set by a widget inside a lower index.

We can solve this by the following:

1. remove xxxFacets, but instead put an empty (truthy) value in a refinement on initialization
2. facets gets set based on the refinement only, and does not have getters & setters anymore

Right now we are working around this issue by setting the refinement to empty on getConfiguration and are going to change the toggleFacetRefinement & removeFacetRefinement functions to keep an empty array instead of clearing. This works, but could be brittle.