Implement dynamic SVG icon colorization system

- Add SVGColorize class for theme-based icon colorization using lxml
- Create unified svg/ directory with all icons from light/ directory
- Update icon_manager.py to support dynamic SVG colorization
- Add ICON_COLORS dictionary mapping CSS classes to theme colors
- Implement _process_svg_icon and _process_regular_icon methods
- Update image_path_manager.py to prioritize svg/ directory
- Support for ICON_1, ICON_2, ICON_3, ICON_4, SPYDER_LOGO_WEB, SPYDER_LOGO_SNAKE classes

This system allows SVG icons to automatically adapt to the current theme
by replacing CSS class names with actual color values from SpyderPalette.

Author: conradolandia