Last screen: perform blurring within KeyguardImageService
This will remove overhead from lockscreen as it doesn't need to blur
captured screen itself. Will also: 
- speed up lockscreen rotation changes
- fix issues on some JellyBean devices where blurring seemed to be
performed also when screen turned on
Merge branch 'kitkat' of https://github.com/GravityBox/GravityBox.git into kitkat