add high-end graphics option for low-memory devices

it enables high-end visual effects such as
transparent status/navigation bar for low
memory devices

depends on:

https://gerrit.omnirom.org/#/c/7262/

Signed-off-by: Humberto Borba <humberos@gmail.com>
Change-Id: Ia314fd27f471de1de04edca11364c04bde1724c9