Add SinatraApp class/test, add sinatra and rack/test gems
More configuration

 - I added some dummy views to make sure they are loaded into the browser
correctly.
 - I made SinatraApp inherit from Sinatra::Base
 - I added a config.ru file so the app can be launched with rackup -p 4567
Add capybara gem to test-drive views
Refactoring

Apparently I don't have to require "sinatra/base", even though the
documentation specifically says to use that instead of "sinatra".
My test doesn't work with only "sinatra/base" though, and Andrew also
is requiring "sinatra" instead of "sinatra/base".
Also, I set up sinatra_app_spec to work with Capybara, which apparently
uses Rack::Test by default (so I removed the configuration for that).
Add Browser IO class with first test