Effect "Filter" to filter colors before sent to LEDs

[nitz]

https://trello.com/c/wfORjubq/87-effect-filter-to-filter-colors-before-sent-to-leds

Could do an effects 'stack' too.

• Fade screen brightness when not in use, but be able to jump back to user's brightness when activity resumes.
• CIE1931 Filter