Allow to change limit

[nichtich]

We sometimes get timeouts with DANTE API for long lists of vocabularies. Setting the limit to be passed to
https://github.com/gbv/cocoda-sdk/blob/master/src/providers/concept-api-provider.js#L174 might help.

[stefandesu]

We want all of the vocabularies though, right? Also, where did you notice the timeouts? jskos-proxy requests the vocabularies from DANTE on the server and caches them, so that the client shouldn't notice any of that. I implemented it that way specifically because DANTE API often takes a long time to serve the list of all vocabularies (for reasons unknown to me).