Make space hierarchy a treeview

src/components/views/spaces/SpacePanel.tsx

@@ -272,6 +272,7 @@ const SpacePanel = () => {
                     <ul
                         className={classNames("mx_SpacePanel", { collapsed: isPanelCollapsed })}
                         onKeyDown={onKeyDownHandler}
+                        role="tree"
                     >
                         <Droppable droppableId="top-level-spaces">
                             { (provided, snapshot) => (

src/components/views/spaces/SpaceTreeLevel.tsx

@@ -328,7 +328,7 @@ const SpaceTreeLevel: React.FC<ITreeLevelProps> = ({
     isNested,
     parents,
 }) => {
-    return <ul className="mx_SpaceTreeLevel">
+    return <ul className="mx_SpaceTreeLevel" role="group">
         { spaces.map(s => {
             return (<SpaceItem
                 key={s.roomId}