make 'alpha' use dynqt (more backends)
add lots of comments / docstrings
add keyboard shortcut Shift-D for DEBUG toggling
highlight header/footer rects in green
also slow down animations with Shift-D
extract module 'decomposer' (Presentation init)
make tests run from any directory
move extract_patches() call into decomposer
layout: weaker criterion for mean section size
fix output of statistics after decomposing
properly detect frame background colors
make ChangedRect more compatible to Patch
call detect_navigation after duplicate detection
extract decomposer.load_presentation()
add unit tests for rendering results
fix unpickling of Frame backgroundColors
implement RandomForestClassifier for navigation

* training / classification via shift-click
* TODO: classifier persistence
* TODO: training data persistence
* TODO: more features (presentation-based)
give immediate feedback after RF training
add Patch.occurrenceCount as classification feature
collect actual occurrences, not just their count