Added script to automate the uploading of internal beta to HockeyApp

Added `generate-build-and-upload-to-hockey-app.rb` which will automate the normal steps taken to upload the internal beta. The script will:
1) Attach the date to the current internal version of the app.
2) Archive the app and generate the IPA and dSYM files needed for upload.
3) Upload the IPA and dSYM to HockeyApp and flag the latest version as mandatory (Note – no email notifications are sent out as a part of this script. The reason for this is that we want to verify our uploaded builds by hand briefly and then once verified we can easily send out email notifications over at HockeyApp.)

To use the script you need to add a `.hockey_app_credentials` file to the root directory of the project and add in `HOCKEY_APP_TOKEN=tokenhere` where the token comes from https://rink.hockeyapp.net/manage/auth_tokens.

cc @astralbodies