Add Extra Dark theme (#955)

* added new theme - night

* removed a unused field

* fixed a typo from previous change

* night theme in login window

* changed name

changed the theme name from "Night" to "Extra Dark"

* changed the theme name

* Update index.js

* Rename night.js to extradark.js

* trying something

* formatted

the JS build was failing because I haven't formatted the index.js file with prettier. I got to know about this now.
I think now it will be resolved.

ui/src/themes/extradark.js

@@ -0,0 +1,35 @@
+import blue from '@material-ui/core/colors/blue'
+
+export default {
+  themeName: 'Extra Dark',
+  palette: {
+    background: {
+      paper: '#000000',
+      default: '#000000',
+    },
+    primary: {
+      main: '#0f60b6',
+      contrastText: '#909090',
+    },
+    secondary: blue,
+    type: 'dark',
+  },
+  overrides: {
+    MuiFormGroup: {
+      root: {
+        color: 'white',
+      },
+    },
+    NDLogin: {
+      systemNameLink: {
+        color: '#fff',
+      },
+      welcome: {
+        color: '#eee',
+      },
+    },
+  },
+  player: {
+    theme: 'dark',
+  },
+}

ui/src/themes/index.js

@@ -1,6 +1,13 @@
 import LightTheme from './light'
 import DarkTheme from './dark'
+import ExtraDarkTheme from './extradark'
 import GreenTheme from './green'
 import SpotifyTheme from './spotify'
 
-export default { LightTheme, DarkTheme, GreenTheme, SpotifyTheme }
+export default {
+  LightTheme,
+  DarkTheme,
+  ExtraDarkTheme,
+  GreenTheme,
+  SpotifyTheme,
+}