put back Xcode ignore to Objective-C.

Majority of Objective-c developers are working in Xcode with Objective-C, so it make sense to keep default Xcode ignore. When user select Objective-C ignore template, it should ignore all possible variants (Xcode and AppCode). And apps can be submitted to app store only with Xcode, so Xcode-file should be ignored.

Fixes #1016