add device gem
add files generated when rails g devise:install
add configuration for device
add files when generating 'rails g device user' and 'rake db:migrate'
add navigation as signup and signin links
add before_action method for user to signin
modified sign_in and sign_up url paths to login and register
modified user password length
add username to users with migration and migrated to db
 add device files and reverting username migration
Merge branch 'devise'