Support having the same map multiple times + custom map naming

[Glodenox]

Right now, it is not possible to add the same map layer twice. OpenLayers refuses this with the message that a map layer with that name already exists. Because sometimes you sometimes want to have only a certain subset of layers, it would be useful if users can add the same map multiple times. Each map instance could then be set to show different map layers.

To be able to distinguish between the different versions of the map layers, users would need to be able to adjust the map name for that instance. This could probably be taken as a chance to visually overhaul the map layer configuration. I'm thinking about replacing the icon for hiding/showing with a simple checkbox instead, as it is the most common action there. Supporting layer nesting would probably also make sense.