Fixed Issued 69, plugin now works with Xcode 6.0.1

Updated project settings, turned off debug user interface setting in
scheme which cased the plugin to crash and removed and then re-added the XCFPreferencesWindowController.xib
resource. For some reason, it was not being copied to the plugin’s resource folder upon building, which was causing the problem. All three changes seemed to be needed to get the plugin working.