Requiring Ruby 2.0

... after a conversation in
https://github.com/jenkinsci/selenium-tests/commit/d6f95901758ce9446fb9392257f1989eb537abb6

I think it's good to be restrictive on Ruby versions to ensure
consistency of behaviours.
add lib to the load path for simpler loading of lib/**/*.rb
Refactored Docker support.

Now allowin individual fixture to come with their own Container subtype so that it can be better encapsulated and reused from different steps
using the load path to simplify relative references
adding the project creation logic
Making the format verbose so that RVM would understand it