Themes: Make notification list bg themeable

Thanks Thomas Ekelschot :)

Screen of themed resource https://imgur.com/c8t1Zn0

PS2: Add Clark's proposed changes
PS3: Cleanup old color resource in main xml
PS4: Add informative screen

Signed-off-by: Carlo Savignano <stevewatersy@gmail.com>
Change-Id: I8eb4427747c3eb035b416860c3ca47122e45c16f
Themes fix home button

Inspired from commit authored by linuxman94
https://github.com/AOSPA/android_frameworks_base/commit/ebc912f0e2e97c3de1dfbff6aac1785ce75b7b33