ReplayGain support + audio normalization (web player) (#1988)

* ReplayGain support

- extract ReplayGain tags from files, expose via native api
- use metadata to normalize audio in web player

* make pre-push happy

* remove unnecessary prints

* remove another unnecessary print

* add tooltips, see metadata

* address comments, use settings instead

* remove console.log

* use better language for gain modes

ui/src/audioplayer/PlayerToolbar.js

@@ -5,8 +5,13 @@ import { LoveButton, useToggleLove } from '../common'
 import { keyMap } from '../hotkeys'
 import config from '../config'
 
-const Placeholder = () =>
-  config.enableFavourites && <LoveButton disabled={true} resource={'song'} />
+const Placeholder = () => (
+  <>
+    {config.enableFavourites && (
+      <LoveButton disabled={true} resource={'song'} />
+    )}
+  </>
+)
 
 const Toolbar = ({ id }) => {
   const { data, loading } = useGetOne('song', id)
@@ -15,6 +20,7 @@ const Toolbar = ({ id }) => {
   const handlers = {
     TOGGLE_LOVE: useCallback(() => toggleLove(), [toggleLove]),
   }
+
   return (
     <>
       <GlobalHotKeys keyMap={keyMap} handlers={handlers} allowChanges />