Add check for latency for all serial connections

[csherstan]

To ensure good performance, all serial connections should be set to low latency. We should add a check for this for Dynamixels and Creates.

To check latency of a particular serial port:
cat /sys/bus/usb-serial/devices/ttyUSB0/latency_timer
To change the latency we can do

sudo apt install setserial
setserial /dev/ttyUSB0 low_latency

At present the default value is 16, but it should be set to 1 by the setserial command. If the computer is restarted or the device removed and reinserted it will reset to the default. Not sure how to correct this.

This works on Debian variants, but I don't know about OSX or Windows.