Revert "Remove user model"

This reverts commit 3ab577f22e0a016a04459b4c04b15e3c8daf9ba0.

Conflicts:
  app/models/user.rb
Revert "Execute 'rails g devise user'"

This reverts commit be23fd9e4a1a0e4993d73ab0d7d64ed51ec0c2c6.

Conflicts:
  app/models/user.rb
  config/routes.rb
Execute 'rails g devise user'
Execute 'rake db:migrate'
Fix login path