Add gradient option for album art and use it by default

Instead of blurring, extract the vibrant colors from the album art
and apply it as gradient, where it transitions top to bottom
from light to dark.

As many people love blur, give them the option to toggle between them.

Change-Id: I05d00c41db3e7dc6a8bfc6b1aa4972c6b594e7f9
Signed-off-by: Alexander Martinz <amartinz@shiftphones.com>
Signed-off-by: Joey <joey@lineageos.org>