implement command queue for shift lights

[rickyelopez]

Usually, you want shift lights to blink at you when it's time to shift. There's not really an easy way to make the shift lights stay on for a specific amount of time without using delay() calls, which is unacceptable since it slows down the whole code.

• Implement a "command queue" where commands to the shift lights can be pushed
  • each command in the queue should have a timestamp
  • a timeout should be defined
  • any command that has expired (i.e. threshold passed) should be ignored
  • if more then x commands in queue, clear queue so as not to get bogged down or laggy