Rework VDisk donor's representation on Storage/Nodes page

[va-kuznecov]

Now it's impossible to distinguish VDisk link-to-donor and VDisk itself. In UI link-to-donor looks like VDisk. So I want to propose:

1. don't draw VDisk's donors on new location near new VDisk. It seems to be important to show donors list, but maybe VDisk's description is more appropriate place for the list
2. on the previous place, there the donor itself lives, show visually mark it as donor. Maybe yellow color, maybe paint it in stripes