improve collapsed LHS implementation - split the tooltip into its own component; position it with javascript as overflow-y + position absolute = clipping hell; preserve the collapse state between MatrixChat re-renders; fix positioning of the 'show' button; switch to dispatcher for show/hide LHS; remove errant scrollbars

src/skins/vector/css/organisms/RoomDirectory.css

@@ -57,7 +57,7 @@ limitations under the License.
 }
 
 .mx_RoomDirectory_tableWrapper {
-    overflow-y: scroll;
+    overflow-y: auto;
     -webkit-flex: 1 1 0;    
     flex: 1 1 0;
 }