Changes in this commit include:
- Add Core.cleanup() and CoreBaseModule._cleanup() functions
- All builtin modules now clean and free any nodes
- Reduce code duplication in src/core.gd by not writing the same code for all builtin modules but instead iterating through a array
The config key 'logui_background' has been removed in favour of 'logui_background_color' and 'logui_enabled'. 'logui_enabled' controls whenether LogUI is displayed or not. To achieve the background transparency, 'logui_background_color' should be set to 'Color.TRANSPARENT'.
