Change Admin Volumes to a tabgroup

Currently there is no Snapshots area in Admin Volumes. In order to
enable the reset snapshot state feature, We need a new tab for Snapshots
in the same manner as what's in Project Volumes. This submit is part 1
of the work, which is to refactor the Volumes panel and make it a
tabgroup. This is so that we can add another tab for Snapshots later on
(in part 2).

Note that these are only structural changes. There are no content
changes.

Partial-Implements: blueprint cinder-reset-snapshot-state
Change-Id: Ibadc4151e698dc6ea99009f6a63fc89c6d001946
Updated the steps of the tutorial

The existing tutorial is outdated, hard to follow and does not
work.

Update or rewrite the steps of the tutorial to create a dashboard,
a panel, a tab group, a tab and a table which contains some data
from backend a table which contains some data from backend.

Make sure the steps work.

Updated the brief explanation as well.

Closes-Bug: #1298490

Change-Id: I7c6769fa6b8cd5488afc03e8a284342549a6745f
Merge "Updated the steps of the tutorial"
Merge "Change Admin Volumes to a tabgroup"