Massive refactor

- Use contextual namespaces within Flarum\Core
- Clean up and docblock everything
- Refactor Activity/Notification blueprint stuff
- Refactor Formatter stuff
- Refactor Search stuff
- Upgrade to JSON-API 1.0
- Removed “addedPosts” and “removedPosts” relationships from discussion
API. This was used for adding/removing event posts after renaming a
discussion etc. Instead we should make an additional request to get all
new posts

Todo:
- Fix Extenders and extensions
- Get rid of repository interfaces
- Fix other bugs I’ve inevitably introduced

js/forum/src/components/settings-page.js

@@ -113,7 +113,7 @@ export default class SettingsPage extends UserPage {
         label: 'Allow others to see when I am online',
         state: this.user().preferences().discloseOnline,
         onchange: (value, component) => {
-          this.user().pushData({lastSeenTime: null});
+          this.user().pushAttributes({lastSeenTime: null});
           this.save('discloseOnline')(value, component);
         }
       })