Add a variant to a plugin, called a 'module.' It is designed for
features that are build-in to the standard UI (i.e., not installed
dynamically), but can still utilize the modular nature of UI
plugins. It works exactly the same way as a plugin, except:
-Modules are added to modules/ folder
-Modules are registered in modules/modules.js
-No config.js (no need for metadata, since they are built-in features)
- /ui/modules/ folder will not be touched by the build system, so any modules
are committed directly to the ui/ folder. In other words, modules are
not installed automatically.
