Allow selecting multiple entity instances in ArMemMemoryViewer

Currently, the MemoryViewer only supports one InstanceView, i.e. you can only watch the values of one entity/snapshot/instance. However, we might want to allow watching more than one instance. This would require dynamically adding and removing InstanceViews plus GUI elements to control them (similar to etherkitten).

This might require some discussion/design beforehand.

added module::armem label

@RainerKartmann can you elaborate what is meant with this issue? This would seem suitable for a HiWi task but instructions unclear

Does this clarify things?

changed the description