evdev MULTIKEYS support

[freevo_confi.py]
+ global vars
+ small guide how to configure multikeys support
+ short comment in addition to existing one (EVENT_DEVS)

[evdev.py]
+ differentiation for error code 19 to catch when the usb hid device was lost/disconnected

[inputhelper.py]
* moved device init to initdev method (for future using)
+ device-related class vars, now we can really use more that one hid device simultaniously
+ store the dev path to reconnect to the same device on error
+ MULTIKEYS support
! self._movements now are device-related