Persist the locale to the store and localStorage

The locale will be set whenever a localized URL is loaded, provided
the locale is supported (i.e. we have localized content for that
locale). The locale is persisted to localStorage to survive site
reloads.

lesson_index.js

@@ -57,7 +57,8 @@ import l3_complete from './3/14-lessoncomplete.md'
 // chapterList is an ordered array of chapters. The order represents the order of the chapters.
 // chapter index will be 1-based and not zero-based. First chapter is 1
 
-export default {
+// English (source for all translations)
+const en = {
   1: [
     l1_overview,
     lessonoverview,
@@ -114,3 +115,7 @@ export default {
   4:[],
   5:[],
 }
+
+export default {
+  en
+}