Channel menu updates

* Changed menu palette to 16 unique colors, named A-P
* Changed (OFF) button to "Disable" button below colors.
* Channel colors and labels are now stored in JSON instead of hardcoded in markup.
* All components with any defaults specified now use "A" which isn't great.
Can you file a follow-up bug about this default problem? All defaults will be set to the same channel with this change. We can do a simple cycle through available letters for components with >1 default.