Adds rspec color output settings

Adds color setting for rspec output to the project.
Moves rails_12factor to production group to suppress output in rspec

rails_12factor includes rails_stdout_logging as a dependency, which
causes verbose logging output to appear when rspec is run. This commit
moves this gem to the production group so verbose logging doesn't
appear when running rspec in development.
Removes unused fixtures

With the move to VCR, fixtures are no longer needed because VCR has its
own cassettes in place.
Moves rspec configuration to readme

Instead of constraining the user to specific style of rspec
configuration, this commit removes color coding configuration from the
spec_helper and instead provides more information on how to configure
rspec output in the readme.
Readme copy changes

Updates text in the readme.
Merge pull request #294 from codeforamerica/rspec-formatting

Rspec formatting