Use inotify listening devices path changes to implement hotplug support.
The new hotplug thread is also an event loop, so the interval value has
no effect.
The evdev is now open on demand.
Fix libinput_interface object life-time.
Use libinput event for keyboard state updates.
The state will update when CAPS_LOCK, NUM_LOCK or SCROLL_LOCK has been
released,
`interval` will have no effect after this change.
