added theming support with 3 themes (only 2 selectable for now)

switched from css to scss default style system

cleaned up unused code in app component

upated youtube search results styling

downloading video from home screen now shows local progress bar under that video

src/themes.ts

@@ -0,0 +1,22 @@
+const THEMES_CONFIG = {
+    'default': {
+        'key': 'default',
+        'background_color': 'ghostwhite',
+        'css_label': 'default-theme',
+        'social_theme': 'material-light'
+    },
+    'dark': {
+        'key': 'dark',
+        'background_color': '#757575',
+        'css_label': 'dark-theme',
+        'social_theme': 'material-dark'
+    },
+    'light': {
+        'key': 'light',
+        'background_color': 'white',
+        'css_label': 'light-theme',
+        'social_theme': 'material-light'
+    }
+};
+
+export {THEMES_CONFIG};