Feature/operation exists in objectmanager queue

Finds any operation in the object manager's operation queue whose requests match the specified HTTP method and path pattern and returns YES if one exist.
 
 Paths are matches against the `path` of the `NSURL` of the `NSURLRequest` of each `RKObjectRequestOperation` contained in the receiver's operation queue using a `RKPathMatcher` object.
 
 @param method The HTTP method to match for the cancelled requests, such as `RKRequestMethodGET`, `RKRequestMethodPOST`, `RKRequestMethodPUT`, `RKRequestMethodPatch`, or `RKRequestMethodDELETE`. If `RKRequestMethodAny`, all object request operations with URLs matching the given path pattern will be cancelled.
 @param pathPattern The pattern to match against the path of the request URL for executing object request operations considered for cancellation.
 
 @see `RKPathMatcher`