Added instructions to the README for how to get the google services configuration files for analytics. Removed (and ignored in future) the empty config files. Note: empty folders are ignored in git, so added an empty file `.exist` to the android folder so that it will be there as a place to hold the actual google services file.
Finally added the xCode scheme for the app that you need for newer versions of xCode.
I also decided to add the Pods directory to gitignore. It bloats the ScratchJr repo. This does mean that people will need to install cocoapods and run `pod install` the first time they build scratchjr.
