Jringle/fps debug

[ringlej]

@axelson This will log every second the number of frames rendered.
Could you run this against the code you are having issues with?
Also with SCENIC_DRIVER_LOCAL=glfw for comparison against the non-cairo code on host,
and SCENIC_DRIVER_LOCAL=drm for comparison against the non-cairo code on rpi3

On the application config for the viewport set the debug_fps option to 1 or 2 to get debug fps output:

config :hello_scenic_full, :viewport,
  name: :main_viewport,
  size: {800, 600},
  theme: :dark,
  default_scene: HelloScenicFull.Scene.Components,
  drivers: [
    [
      module: Scenic.Driver.Local,
      name: :local,
      window: [resizeable: false, title: "hello_scenic_full"],
      on_close: :stop_system,
      debug_fps: 2,
      layer: 1,
      opacity: 180,
    ]
  ]

[ringlej]

@crertel Please re-review. I added another commit