Add Status bar transparency, (1/2)

Home screen transparency "support" is ported from BeerGang:

https://github.com/BeerGang/android_frameworks_base/commit/848ebdbc3858522817032ed5d3d21598144acb15
https://github.com/BeerGang/android_frameworks_base/commit/9e86dd70c3b9f41ca6d85d23c10d92f8f333f840
https://github.com/BeerGang/android_frameworks_base/commit/aedcf60aa52861e25dd23d8bbd801b2cdcec68f7

Statusbar transparency code is inspired from Beergang