[5.1.1] modify application layout
[5.1.2] add bootstrap

 * add bootstrap
 * create skeleton to learn scss
[5.1.3] add header and footer partial erb
[5.2.2] modify to scss syntax
[5.3.2] modify to use routes methods at config/routes.rb
[5.3.3] use named routes at header / footer
[5.3.4] refactor test

 * use before and subject
 * remove string argument from testcase
 * add spec utility
[5.4.1] generate Users controller
[5.4.2] generate Signup URI

 * generate controller Users
 * add integration_test
 * add link to signup page