Try to make app work on Heroku

Prevent Heroku from trying to initialize the Rails environment before
precompiling assets.
Add unicorn configuration file

Try to make app work on Heroku with Unicorn web server
Simplify custom scss file
Change routes

Define named route for home
Change header layout

Use named route: root_path
Change views
Generate integration test for links on homepage
Add route for signup page
Change signup link in homepage

Link to signup page
Add view for signup page
Add test for validation of user's name
Validate the presence of user's name
Validate (with test) the presence of user's email
Validate length of user's name and email

With test
Validate (with test) email format
Validate the uniqueness of email addresses
Add index on email of user
Downcase email address before save
Add secure password

Add password_digest column to 'users' table

Add has_secure_password to model
Validate password length greater than minimum