[Feature] Include overall detection FPS on System page.

[ccutrer]

The /api/stats endpoint includes a top-level detection_fps field, that is the sum of the detection_fps from all the cameras. It would be nice if this was displayed somewhere on the System page, so you don't have to do the summing yourself in the UI (which is a pain with 33 cameras!). Maybe even better would be if detection fps was kept track of per detector, so if you have multiple corals you can see that load is being evenly divided among them.