More saturated icons go better with the new editor theme.
These color changes only apply when using a dark theme.
The editor icon saturation can still be adjusted in the Editor Settings.
Setting the editor icon saturation setting to 0.77 should roughly match
the old icon saturation.
The functionality is similar to how `doc_classes` are retrieved per module.
The build system will search for custom icons path defined per module via
`get_icons_path()` method in `config.py` or default icons path.
If such paths don't exist, only the editor's own icons will be built.
Most module icons were moved from editor/icons to respective modules.
