Attempt to fix issue https://github.com/pluyckx/kam/issues/6

 * Add a udevmonitor class which uses the command udevadm monitor
   to monitor usb devices
 * Use udevmonitor in the keyboard and mouse checks to reload the
   configuration if a usb device is added or removed
 * ignore all errors on usb removal -> this we should fix

Signed-off-by: Philip Luyckx <philip.luyckx@gmail.com>