Updated OS switcher to try and auto-detect what operating system the visitor is using.

This will only take place if an OS hasn't already been selected (i.e. when the cookie is not present).
Updated standard app tutorial to include some windows specific tips.
Added a line to instruct the student to remove the index.html file, and added instructions for the coach to discuss route orders and static files.
* Re-ordered the steps to setup git first. 
* Also added instructions to setup .gitignore for logs, tmp files and uploads.

* Added tip for coach to discuss why Heroku uses Postgresql.
* Added some details on why rails_12facter is being included.
Added some closing notes on Heroku's ephemeral storage and linked to ways on how to work around this (S3).
Revert to upstream change for index.html - someone beat me :)