SystemUI: Fix notification header disappearing on tablets

For some reason, the notification panel header has weird dimensions
when it has anything else than its original ColorDrawable as
background, and only on tablets.

We workaround this by not changing the drawable until requested.

Change-Id: Id76a5dcacf59c35b2e49681d6eeb4e828f7cbc58
Re-implement gesture lockscreen into Keyguard

Change-Id: I43a1307d355ad9cd8f3c3b94d05e954f23289ae3
Re-implement lockscreen wallpaper into Keyguard

Change-Id: Ic636f362b1eda3227c34bc6fcf688372b948d40f
Add missing gesture unlock stuff