Replace kebab menu in file editor with on hover menu (#4624)

Replace kebab menu in file editor with on hover menu by refactoring page
editor's menu into a new component. In mobile sizes, the hover menus are
always visible.

frontend/public/locales/en-GB/translation.json

@@ -90,6 +90,11 @@
   "moreOptions": "More Options",
   "editYourNewFiles": "Edit your new file(s)",
   "close": "Close",
+  "openInViewer": "Open in Viewer",
+  "confirmClose": "Confirm Close",
+  "confirmCloseMessage": "Are you sure you want to close this file?",
+  "confirmCloseCancel": "Cancel",
+  "confirmCloseConfirm": "Close File",
   "fileSelected": "Selected: {{filename}}",
   "chooseFile": "Choose File",
   "filesSelected": "{{count}} files selected",