Feature/gallery view (#6578)

* add gallery view, display images in grid layout

* remove redundant code

* clean up redundant code, improve responsive gallery

* improve gaps in gallery

frontend/src/components/cur-dir-path/dir-tool.js

@@ -113,7 +113,7 @@ class DirTool extends React.Component {
 
     if (isFileExtended) {
       return (
-        <div className="d-flex">
+        <div className="dir-tool">
           <MetadataViewToolBar viewId={viewId} />
         </div>
       );