only transform the bitmap drawable if we really have to
use less locks
fix a race condition on the running thread to download when adding/removing/adding quickly the same job
better job removal race fix
rare crash fix
fix the reuse of a job so it can't be added and aborting at the same time
fix target index not accurate when quickly adding/removing items, keep removed job and marked them as not needed anymore
we need a concurrency handler for the job
implement a proper PictureJob test