Use Rails.root.join without lambdas to declare dashboards_views_path and jobs_path inside configuration.rb

This is continuation of #52. 

#52 fixed issue when `Rails.root` was not initialized during invocation of `Configuration` initializer. Because of that we can switch to using `Rails.root` for initializing of `dashboards_views_path` and `jobs_path` config options.

Best wishes, 
Alex L.