High prio:
- Fix TWAIN

Mid prio:
- Don't set whole window to inactive when loading page, just display a "working" image and queue the rendering operation. If another rendering request comes in, cancel the active one.
- Fix backtrace window on windows (spawn async?)
- output pane in separate window
- installation of tesseract langpacks through packagekit?

Low prio:
- replace all (how to integrate it in the UI?)