Add a bit of filtering to dashboard display to make identifying changed signals easier

[peplin]

Because the dashboard updates so quickly, it can be easy to miss when a signal changes if it goes right back to the previous value. For example, when trying to identify a CAN message for a button press, the values over time might be 0 0 0 0 0 0 0 0 1 0 0 0 0 0 where it's marked as 'pressed' for only a split second. We'll have to think a bit about how to do this filtering without making it inaccurate or "floaty" feeling, but I imagine this is something others have worked on before.