Fix: Correct possible null pointer when enabling see through lockscreen

PS2: Remove unused variable

Change-Id: I28884cb18964b273539261b8c0f72cedf2e60666
Frameworks: Lockscreen Blur

  If user selects "See through" under screen security,
  the locksceen background will now appear transparent
  with the content behind it blurred.

Modificaitons made to the orginal commit to support Hammerhead and Flo.
It seems full HD images causes rendering artifacts. To prevent this,
we scale the image size to something more manageable.

PS2: Reduce calls to System.Settngs
     Move bitmap scaling to DisplayPowerController
PS3: Fix styling
PS4: Fixes: 1. Black wallpaper after turning off see through
            2. Wallpaper flicker on unlock when blur is enabled
PS5: Ignore status bar and nav bar when capturing screenshots
PS6: 1. Remove content observer and unnecessary calls from viewManager
     2. Restructure the flow of setting the custom image
         * now closely follows setting album art as lockscreen image

Change-Id: Ie72bab697726af5e145bd0192980885ea7222ecd

Conflicts:
	packages/Keyguard/src/com/android/keyguard/KeyguardViewManager.java
	policy/src/com/android/internal/policy/impl/keyguard/KeyguardServiceWrapper.java
	services/java/com/android/server/power/DisplayPowerController.java