Use an immutability library for arrays and objects in SearchParameters

[bobylito]

Although the state is mostly immutable in SearchParameters, the inner structures based on array and objects are not due to their nature of native objects. It would be nice to use a library like Immutable to change the implementations of those structures. We could also benefits from data structures like Set or OrderedMap.

We should also make sure to leak the very minimal amount of abstractions to the users...

[bobylito]

Conjunctive, disjuncive and exclude facet refinements should be stored in sets

[Jerska]

Pretty scared of the JSON.stringify(state) of this. Agreed if we handle URL parameters with the helper.

[bobylito]

I have the same kind of fear, that's why I explicitly mentionned that we shouldn't leak to the user. It's for internal purpose only.

[vvo]

I do not understand the fear around JSON.stringify, where it is (would be?) used?

thx

[bobylito]

If we expose objects that are much more complex that plain objects or array, what would their serialization? That's the question. I guess you question is right in the sense that if we stringify an object it'll be pure json. Then no need to worry... yet I think it's better that the users thinks the values are simple js structures.

[bobylito]

see #105