V3 mac secure input

Hi!

The main feature of this pull request is the implementation of `NSSecureTextField` on Mac, so now CCEditBox shows a password field when `InputFlag::PASSWORD` is set:

![](http://mazyod.com/images/example-NSSecureTextField.png)

Another important change is the removal of `CCCustomNSTextField` class. It was apparently copied from the iOS implementation, but `UITextField` and `NSTextField` are **vastly** different.

Two other minor changes exist, fixing the `init` method to be according to the Objective-C convention, and removing the call `self.textField = NULL`, since it's dangerous to call setters in dealloc. Instead, the ivar should be released manually.

Best,
Maz