Use apollo-client without `apollo-link-http`

[tchak]

I am implementing my own link (not based on http). If I exclude apollo-link-http from packages (to save some space) the apollo service will crash because unable to load apollo-link-http. Would you accept a PR to have a BaseApolloService without apollo-link-http (and maybe without cache) from which ApolloService will inherit and from which users can inherit in advanced cases?

[bgentry]

Yes, the design you describe makes a lot of sense. Ideally we should support the most common use case out-of-the-box with little/no required config, but also make it possible to serve more advanced use cases like yours.

Regarding the name, this is somewhat unconventional but what do you think about ApolloBaseService instead of BaseApolloService? I like it because it keeps the Apollo prefix.

[viniciussbs]

If this base service is a mixin, you should take a look at #139.