issue #2371: Updating multi-platform-template for iOS and Mac
issue #2371: Deleting cocos2dx/proj.ios and cocos2dx/proj.mac since it isn't needed anymore, moving the prefix header file to previous folder.
issue #2371: Using the same prefix header for iOS and Mac.
Merge pull request #3077 from dumganhar/iss2371-template

Updating multi-platform-template for iOS and Mac, and deleting cocos2dx/proj.ios and cocos2dx/proj.mac since it isn't needed anymore, moving the prefix header file to previous folder.