Move volume snapshots table to volumes panel

Now that instance snapshots are just images, the images & snapshots
page only has images and volume snapshots. This is an odd combination.
I think we should now move volume snapshots to the volumes panel,
since a volume snapshot is tied to a volume.

Closes-Bug: #1190843
Change-Id: I3e12cec8b859a30db9f131e9889a92277e064086
Merge "Move volume snapshots table to volumes panel"