Neighborhood view layout can crash the page

[yGuy]

Describe the bug
In case of really really dense graphs, the neighborhood view (when used with more than one layer) can become a bottleneck and since it seems to be running the layout on the main thread, it can block the page.

To Reproduce
Steps to reproduce the behavior:

1. Use a really really dense and large graph
2. Click on a node
3. Go to the overview and pull the slider down
4. Observe the page freezing

Expected behavior
For truely large graphs, we should not be showing them in the overview anyway. But if we do, we should run the layout in a worker.