Add double tap to sleep gesture, (1/2):

Thanks to CyanogenMod:
https://github.com/CyanogenMod/android_frameworks_base/commit/2554662f09061709d9886c25de68243107f91d0a
https://github.com/CyanogenMod/android_frameworks_base/commit/15cea186e6f208f590b933d1531e7e1f1e4e52ed