VS Code style three-column layout plug-in

Key features

• The resident Explorer file tree on the right (VS Code official seti file type icon, expand/collapse, new file/folder, refresh, collapse all, draggable/collapse panel)
• The right column requires a new grid track (explorer slot) in the layout shell - completed by ui-layout.patch
• Which workspace/session you switch to, the right column will display the files in that workspace
• Multiple tabs, syntax highlighting, minimap, Ctrl+S, dirty mark, save conflict "reload/force overwrite")