Refactoring test for "unauthenticated users should be redirected to sign_in_path"

Use macros and shared_examples
Refactoring: use macros to simplify set current user in controller specs
Install Capybara
Implement the first feature spec (user sign in)
Rename sign_in_user and logout_user

This is to avoid confusing with `sign_in` macro, which will be introduced later.
Write my_queue feature spec

- Add User#queued_video?
- Hide "+ My Queue" link if the user already queued the video
- Install launchy
Move unnecessary given! into the only scenario
Merge pull request #8 from ascendbruce/week3-part2

Week3 part2