Fix symbol class handling for rendering and broadcasting

[ayezutov]

I was trying to setup a dashboard with MMM-CalendarExt3 and MMM-CalendarExt3Journal. When doing so I could not make the symbols to work. Upon diving deep I have realized that there are some peculiarities about how symbol classes and symbols are being handled.

1. calendarID was not stored on the event in the eventList. This led to always showing the default icon for the module ('calendar'). I have updated line 1072 to explicitly set calendarID on the cloned event. This should be safe as it is removed in line 1076 either way.
2. updated rendering and broadcasting to include configured symbolClass to mimic the native's calendar format.

[B3DTech]

Unfortunately this did absolutely nothing to get my symbols to show up in MMM-CalendarExt3. event color gets passed through fine, but not symbols for some reason.