Add eventClass for customEvents in calendar (#3193)

Hello,
This pull request allows you to add a class to the tr of the event
sought in customEvents. You must enter the class with the "eventClass"
option.

---------

Co-authored-by: TeddyStarinvest <teddy.payet@starinvest.com>

tests/configs/modules/calendar/custom.js

@@ -11,7 +11,7 @@ let config = {
 			module: "calendar",
 			position: "bottom_bar",
 			config: {
-				customEvents: [{ keyword: "CustomEvent", symbol: "dice" }],
+				customEvents: [{ keyword: "CustomEvent", symbol: "dice", eventClass: "undo" }],
 				calendars: [
 					{
 						maximumEntries: 5,