Explicit serial query in OpenNI2Driver::resolveDeviceURI instead of one-time query in OpenNI2DeviceListener::onDeviceConnected & new binary to list devices

 2e79f55 fixes #24. It changes the way serial numbers are handled. Instead of trying only once to retrieve the serial number when a device gets connected, the driver will repeat to try to read serial numbers from connected devices as long as no permanent connection has been established.

The device manager will only know vendor id, product id etc. (things you can see with `lsusb`, too) on startup and the serial number has to be requested explicitly as that requires opening the device.

2290783 adds a binary for convenience that prints out all information about connected devices and their serial number (if the devices could be opened).