Remaining realtime player improvements

[pozitronik]

There is a todo list of remaining improvements for realtime player feature:

• Cover the code with tests where possible.
• Implement the pygame events logic (redraw when resized, add a full-screen mode, add a close window handler, etc). #110
• Improve the control window (add hints and controls captions). #114
• Change options in runtime via menu items.
• Add menu hotkey shortcuts.
• Fix the progress bar ghosting. #96
• Improve the logic of frame drop calculation.
• Check and fix: it seems that sometimes the displayed frame doesn't match with real time expected frame (they don't always have to be the same, but the differences are too great).
• Add the feature to configure manual frame drop. #104
• Improve the status bar (implement a real widget instead of the current stub code). #94
• Perform status messaging via callbacks (to avoid using the widget object itself).
• Show current statistics (framerate, framedrop, memory usage, CPU/GPU usage) in the status bar.
• Display data from the status bar directly on the player window (render text directly on a display).
• Add a new control to select and change the used frame processors set (which may be different for real-time player and render preview).
• Re-implement FrameThumbnail feature #90
• Add different types of targets (a webcam live stream, images folders, etc) and, perhaps, different types of sources. At least, add a 'clear' button to release the curent source image.
• Improve window positioning: save and restore each window's position on close/start of the program. On startup, check, if a window positioned off the screen, and move it to the right place. #98
• Cache already processed frames, and do not reprocess them.
• Cache already extracted frames.
• When the playback is finished, stop it, but continue to process frames into the cache.
• Show overall processing progress.
• Write the documentation.
• Fix: playback startup when frames are unpacking starts another unpacking task -> lock playback until done with cancellation possibility.