Fix popups/Shiny-events for *Src-functions

[trafficonese]

Makes popups and Shiny-click events work with *Src functions.

Also, since layerId is normally a vector, I changed how the attributes in JS are read. They now take the group instead of layerId. But actually I think we should create a random name internally, because now it's not possible to include multiple layers with the same group. Also group and layerId may contain Umlauts or whitespaces, which currently throws this error in a Shiny app:

Warnung: Error in addResourcePath: addResourcePath called with invalid prefix; please see documentation