Add DefaultUIVolume option. Closes #1679

ui/src/config.js

@@ -19,6 +19,7 @@ const defaultConfig = {
   enableStarRating: true,
   defaultTheme: 'Dark',
   defaultLanguage: '',
+  defaultUIVolume: 100,
   enableUserEditing: true,
   devEnableShare: true,
   devSidebarPlaylists: true,

ui/src/reducers/playerReducer.js

@@ -16,7 +16,7 @@ const initialState = {
   queue: [],
   current: {},
   clear: false,
-  volume: 0.5, // 50%
+  volume: config.defaultUIVolume / 100,
   savedPlayIndex: 0,
 }