Provide way to obtain scoped collections

[mitar]

Maybe something like subscriptionHandle.collection[collectionName].find() would be the same as collection.find(subscriptionHandle.scopeQuery()).

I am not sure if this is really the best approach because subscriptions can be for multiple collections and then you have to know how to map to collections. With current approach with scopeQuery we do not care for which collection a document is. This is left to the developer to use properly.

Maybe useful: https://github.com/tmeasday/cursor-utils

[mitar]

See also discussion here: https://github.com/meteor/guide/issues/33#issuecomment-151716789