fix(ui): minor icon inconsistencies and "no missing files" translation (#3837)

* chore(ui): Fix minor inconsistencies

1. The icons in the user menu are a mix of MUI and react-icons. Move them all to react-icons, and use a standard size (24px)
2. On missing files page, provide a custom Empty component that just removes 'yet'

* use RA's builtin support for custom empty message

Signed-off-by: Deluan <deluan@navidrome.org>

---------

Signed-off-by: Deluan <deluan@navidrome.org>
Co-authored-by: Deluan <deluan@navidrome.org>

ui/src/transcoding/index.js

@@ -1,4 +1,4 @@
-import TransformIcon from '@material-ui/icons/Transform'
+import { MdTransform } from 'react-icons/md'
 import TranscodingList from './TranscodingList'
 import TranscodingEdit from './TranscodingEdit'
 import TranscodingCreate from './TranscodingCreate'
@@ -10,5 +10,5 @@ export default {
   edit: config.enableTranscodingConfig && TranscodingEdit,
   create: config.enableTranscodingConfig && TranscodingCreate,
   show: !config.enableTranscodingConfig && TranscodingShow,
-  icon: TransformIcon,
+  icon: MdTransform,
 }