add kded module to sync device LEDs with accent color

Screencast: https://imgur.com/a/sd9Lqz9

Kameleon finds RGB capable LED devices in /sys/class/leds/; typically this would be keyboard backlights but in principle could be anything, provided it has .../multi_intensity.
When setting to enabled, it will apply the current Plasma accent color and automatically update the led color when the accent color changes. Color is reapplied on each startup but not when led color is changed intermediately by a different source.
When setting to disabled, it will write white color once, and then no longer interfere.
Following accent color is enabled by default and can be controlled with this frontend: plasma-workspace!4093 (merged)