Refine layout for output switcher panel

1. only make the output switcher tall enough to show 6.5 devices
2. enlarge album art to 52*52 and keep same size on group panel
3. reduce panel header top padding
4. enlarge slice first item top padding
5. update slider bar right padding
6. update panel height
7. align slice title item left with panel title icon
8. enlarge slice end item right padding

Bug: 156045699
Test: manual test
Change-Id: I51321d98ef483665689b7e258d6071df76382759