Improve Hidden Template Variables

Stems from #84. Hidden template variables are great...

However, they're stored as free text in the .puppetryrc file. I'm not using the integrated git client (so maybe there's some fanciness there to hide them from the repo) but for people using git normally to version control their test suites you have to fully exclude the .puppetryrc file. This means that start up is not as simple as "clone and open in puppetry app".

It would be nice to store just the hidden variables in a separate .puppetryrc.hidden file instead so that the main .puppetryrc could be shared and you'd just have to instruct collaborators to enter those when they first pull the project.