Change tab carousel tab size according to device size

- For phones, the tab width should be 75% of the screen width,
while the tab height should be 50% of the screen width

- For tablets, the tab width should be 66% or 2/3 of the screen
width, while the tab should be square so the tab height should
be 2/3 of the screen width

- Adjust alpha layer to not cover the tab label so that the
"about" and "updates" text will still be on top.

- Added pressed state to fragment overlay in fragment carousel
in phone landscape

Bug: 4689488
Change-Id: Ie7ec3897105abbd195caf0b7f78e380e79f1ddfe