Move NSFetchedResultsController access to iOS-only category

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Remove deprecated +[CoreDataManager instance]

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Simplify CoreDataManager

 - Don't expose helpers that are only used for testing
 - Use TARGET_OS_IPHONE to define differentiating logic

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Use constants when we can

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Update Kiwi specs to use @() over theValue()

Signed-off-by: Stephen Celis <stephen@stephencelis.com>
Update Specs

 - Update to Kiwi 2.2.4
 - Update to us XCTest

Signed-off-by: Stephen Celis <stephen@stephencelis.com>