(feat): fetch chapters on app load to display numNewUnread

- so if any new chapters were released since you last opened the app,
  it will update immediately and indicate if there are any new unread
  chapters as of just now
  - prev would only show new unread chapters since the last time you
    clicked into the manga, which was bound to be out-of-date
  - other than multiple providers, this is the last big, must-have
    feature I really needed to make me consistently return & use this
    app instead of others
    - others are more "nice-to-have" or "very-nice-to-have", but not
      necessarily dealbreakers for me at least

App.js

@@ -15,6 +15,9 @@ persist('@mangaStoreKey', appStore, {
     'mangas',
     'favorites'
   ]
+}).then(() => {
+  // fetch chapters on app load so that numNewUnread is updated
+  appStore.loadFavoritesChapters()
 })
 
 const App = () => (

models/models.js

@@ -83,6 +83,10 @@ const AppModel = types.model('App', {
     self.favorites.splice(self.favorites.findIndex((elem) => {
       return elem === self.selectedManga
     }), 1)
+  },
+
+  loadFavoritesChapters () {
+    self.favorites.forEach((favorite) => favorite.loadChapters())
   }}
 })