Add support for scenes

[blogic]

extend the code to allow triggering predefined scenes/patterns via a given name. These scenes are predefined inside json files located on the FS inside /etc/uledd/*.json.
the format shall be the same as what is currently used on ubus but wrappered inside an outer block such as
{ "scene": "wps", "duration": 60, "priority": 1, "pattern":{ .... the led pattern as passed on ubus} }