SugarRecord results to abstract the response arrays

## What?
Resolves https://github.com/SugarRecord/SugarRecord/issues/44
Realm doesn't use arrays and they use a custom RLMResults because objects are actually references to the real objects on Realm ( to get better performance ). Before this refactor we iterated over those elements in order to create an Array (extra time that Realm tried to avoid with the library). 

I've added a class **RLMResults** which represents query results. It doesn't matter if they come from Realm or they come from CoreData, the format of the RLMResults is the same and you can interact with it like any other iterable class.

## Pending
- [x] Define the protocol
- [x] Implement results array for Realm
- [x] Implement results array for Objective-C
- [x] Modify the fetch to return a SugarRecordResults object instead of an array
- [x] Fixed broken tests
- [x] Add tests for the new features
  - [x] SugarRecordRLMResults Tests
  - [x] SugarRecordCDResults Tests