feat: add dark theme

src/app/settings/settings.interface.ts

@@ -1,4 +1,5 @@
 import { Language } from './language.enum';
+import { Theme } from './theme.enum';
 
 export type VideoPlayerType = 'html5' | 'videojs';
 
@@ -9,4 +10,5 @@ export interface Settings {
     player: VideoPlayerType;
     epgUrl: string;
     language: Language;
+    theme: Theme;
 }