Standardize preposition on context parameter in methods

[brockboland]

As @chillpop noted in a PR comment, we use withContext, forContext, and inContext in various method signatures. Some of these make sense (e.g.: managedObjectOfClass:inContext:) but a lot of them do not (e.g.: arrayForClass:forContext:). Let's review all the method signatures and standardize as much as makes sense.

Deprecate the existing method signatures and have them call the newly-named methods in the first release after this change.