CLASSROOMIO-T-41: Implement dark/light mode switch

Co-authored-by: Rotimi Best <rotimiibitoyeemma@gmail.com>

Merge-request: CLASSROOMIO-MR-8
Merged-by: Digdippa Team <digdippa@gmail.com>

src/utils/functions/app.js

@@ -0,0 +1,7 @@
+export function toggleBodyByTheme(isDark) {
+  if (isDark) {
+    document.body.className = document.body.className.concat(' ', 'dark');
+  } else {
+    document.body.className = document.body.className.replace('dark', '');
+  }
+}

src/utils/store/app.js

@@ -0,0 +1,5 @@
+import { writable } from 'svelte/store';
+
+export const appStore = writable({
+  isDark: false,
+});