[Bug] Icons and Legend improvements

[joywa]

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Describe the bug When using custom images for icons:

1. Depending on the zoom level the node icons are either too big or small, they don't scale appropriately
2. Legend does not include custom images when they are used
3. RDF dataset shows empty labels on the legend

Expected behavior

1. Even scaling
2. Populated icons legend
3. Populated labels for all nodes on the legend