Refactor server to start Rails app with System Testing or Capybara internals

[searls]

Right now, starting a rails server is done by poking around in system testing internals & capybara's server facilities. There's no actually-good reason for this, it was just done because it was an expeditious way to get a consistent-to-system-test server up and running. However, it's the reason we have a hard dep on capybara and selenium-webdriver, which we really shouldn't need to have.

Change would be in this file: https://github.com/testdouble/cypress-rails/blob/master/lib/cypress-rails/starts_rails_server.rb

[searls]

This is now done