Get template values from YAML file

Hello again. As agreed I am sending all of the changes in small batches so we can discuss. I think this is the first step to getting the rest of the code into the project. The idea of this firstone one is fairly simple, getting the maintainer's name, mantainer's email, etc. from a yaml file *_.magnumrc_* if defined, else continue to use the original behaviour.  

The motivation for this is that most likely this values won't change for a user very often and passing them via command parameters can get tedious, this hopes to address this problem. Also, later things like which puppet box wants to be used as default, puppet module directory (for vagrant/serverspec), puppet environment, can bet set.

Also, I noticed that you are already bumping the ruby versions of the gems. So I will not create a pull request for that one.