[db] set up reservations
[controller/view] index, new, destroy of reservation
[chore] delete unnecessary users_decorator
[feature] reservation_job to perform reservatoin
[test] update tests

- remove test for `sign up` (only admin can create users)
- update factories
[style] for switch and time-picker
[device_switch] you can manually pass in operation
[association] a device has_many :reservations
[style] set up global layout
set up guardfile
[chore] foo job only output some hint