Add polygon freehand-drawing

[mfl28]

• Add freehand polygon-drawing mode. Draw JavaFX Path shapes which are automatically converted to polygons upon drawing completion.
• It should be possible to remove vertices using a topological simplification algorithm (using jts). For freehand drawn shapes the simplification should optionally (default=on) run automatically when converting freehand drawn paths to polygons. It should also be possible to run simplification on already created polygons.
• Introduce new EditorSettings settings pane to set the simplification algorithm settings (auto-simplification on/off, simplification tolerance [low->medium->high]).