FPS option in video settings dialog should match hardware capabilities

[mtlynch]

The video settings dialog hardcodes a maximum FPS of 30, but different capture devices have different maximum framerates.

Most HDMI to USB dongles support 30 FPS, but the capture chip we use on the Voyager 1 and Voyager 2 has a max of 24 FPS, so it confuses users to see a different FPS listed in the settings:

We can investigate whether we can auto-detect the device's max FPS from something like v4l2 and then dynamically display that in the slider.