Image pre-processor and post-processor in Display Options

[nostra13]

Add possibility pass pre-processor (process Bitmap before caching in memory) and post-processor (process Bitmap after it was cached in memory cache, before it's displaying and do processing on work thread, not UI-thread, as BitmapDisplayer) in Display Options.

@All_Users Comment here if you need this feature

[nostra13]

4929222

[CapnSpellcheck]

I will find this useful. As I just discovered that the listener is called on the main thread. And I want to create a second bitmap cropped from the first one without having to manage my own thread.