Define statuses regarding the updating of the coursebook

aleksis/apps/alsijil/static/js/vue/alsijil/UpdateStatuses.js

+export const
+    ERROR = "ERROR",         // Something went wrong
+    SAVED = "SAVED",         // Everything alright
+    UPDATING = "UPDATING",   // We are sending something to the server
+    CHANGES = "CHANGES"      // the user changed something, but it has not been saved yet