Rename addObjectsFromArray to addObjects

The name was a misnomer since we really accepted any collection which implements NSFastEnumeration. Since we are breaking things with the next release now is probably a good time to make this change if we want to make it at all.

@jpsim @tgoyne 
Maybe something like "An enumerable type such as NSArray or RLMResults which contains objects of the same class as this RLMArray".