Add classname display overlay - #84

This PR copies over some general changes from #64 as long as that PR is still on hold.

• Add font_scale and thickness arguments to the put_text method
• Add DisplayClassnameOverlay operation that shows detected classes as a big text overlay (see screenshot)
• Fix int parsing of camera_id in all scripts
• Fix assignment of runtime_error in controller.py (the as statement wasn't working as expected)

If you want to test the DisplayClassnameOverlay, add this to the display_ops in run_gesture_recognition.py:

        sense.display.DisplayClassnameOverlay(
            thresholds={
                "\"Sleeping\" gesture": 0.5,
                "Covering ears": 0.5,
                "Covering eyes": 0.5,
                "Facepalming": 0.5,
                "Nodding": 0.5,
                "Putting finger to mouth": 0.5,
                "Scratching": 0.5,
                "Shaking head": 0.5,
                "Waving": 0.5,
            }
        )

We could even add this to the script per default if people like it.