Replace yml file configurations with env variables

This commit removes the need for an api-keys.yml file,
and moves the required configurations to env variables.
It creates a generic settings class that enables ruby-like
access to specific env variables.

Issue #35: Closed
Move sample_data rake task into seeds.rb

Issue #36: Closed.
Merge pull request #37 from rclosner/installation

Work on installation process for new contributors