WallpaperPicker: Destroy cropview to avoid leaks

If the cropview's TiledImageRenderer is rendering threads, the activity
context gets leaked. Avoid that by invoking its destroy in onDestroy() of activity.

Change-Id: I0804c903d14d3f3d13529f0fe90d12784d97e93f
Merge branch 'cm-11.0' of git://github.com/CyanogenMod/android_frameworks_base into cd-4.4