Removed duplicate functions using optional values

Hi!

I have removed all:

```swift
let context = SuperCoreDataStack.defaultStack.managedObjectContext!
```

using swift optional values, so functions like

```swift
class func findFirstOrCreateWithAttribute(attribute: NSString!, value: NSString!, context: NSManagedObjectContext) -> NSManagedObject 
```
Became
```swift
class func findFirstOrCreateWithAttribute(attribute: NSString!, value: NSString!, context: NSManagedObjectContext = SuperCoreDataStack.defaultStack.managedObjectContext!) -> NSManagedObject 
```