Truncate prefixes in container image names

[leth]

Container image names are often quite long, so are truncated in the node view.
Truncation often leaves only the prefix visible, which often offers very little information about the container e.g: google_containers/....

It'd be nice if common prefixes were truncated so that the information-high parts of the name could be seen at a glance, e.g: google.../kube-apiser...

[fbarl]

I got an almost-working prototype very easily a long time ago in experimental-node-labels-central-ellipses branch, but then put it aside as I figured the proper solution might involve a bit more changes (although they might also help us get rid of the occasional label clipping bugs in FF).

Removing myself from this issue now because of its low priority, but might get back to it later if nobody else picks it up before me :)