Update Game_mac build for Xcode 6

Here are some improvements to xcode project in case people need to modify it

* Updates Xcode build settings to allow Game.app to be built on Xcode 6+
* Adds sandbox support to allow games to be submitted to Mac App Store
* Removes build folder that doesn't need to be in source control

Remaining issues:

* App crashes in full screen due to OS X 10.9+ changes. I think this needs to be fixed in OgreOSXCocoaWindow.mm
* App segfaults if closed using window's red X button instead of through game menu. Not sure how to fix yet
Yes, this will be necessary to support full screen games. 10.6 does not have official fullscreen mode. More changes are needed in OGRE part of NeoAxis I think to support this properly.

Latest stats have 97%+ of Macs are running 10.7 or later. https://www.gosquared.com/global/mac/yosemite