Added dark-mode event

[apps-caraga]

Added custom event to be triggered when the darkmode is toggled. Sample use:

document.body.addEventListener("darkmode-toggled", function(event) {
 		if(event.detail.darkModeOn){
			//do something like adjust images to be more visible, or anything else you want to do in the darkmode 😁
		}else{
			//light-mode
		} 
   });