blink1: Document HID buffer sizes.

Adds a comment explaining the mismatch between the blink(1) documentation
and the buffers used with the chrome.hid API.
blink1: Handle undefined results from Blink1.getRgb.

If this API fails the color values returned are undefined. Clamp them to
0 in this case.
blink1: Hide the outline around sliders while dragging.

Modifies the CSS for range input elements to remove the outline when the
element is selected.