Roughly implement routes and data preloading

Only preloading data for basic requests w/o query params, at least for
the moment - if we have to preload for something like
/?q=test&sort=newest, we end up having to duplicate a whole lot of
logic between JS/PHP.

framework/core/src/Api/Actions/Discussions/IndexAction.php

@@ -100,7 +100,7 @@ class IndexAction extends SerializeCollectionAction
         static::addPaginationLinks(
             $document,
             $request,
-            $this->url->toRoute('flarum.api.discussions.index'),
+            $request->http ? $this->url->toRoute('flarum.api.discussions.index') : '',
             $results->areMoreResults()
         );
 

framework/core/src/Api/Actions/Discussions/ShowAction.php

@@ -32,8 +32,8 @@ class ShowAction extends SerializeResourceAction
     public static $include = [
         'startUser' => false,
         'lastUser' => false,
-        'startPost' => true,
-        'lastPost' => true,
+        'startPost' => false,
+        'lastPost' => false,
         'posts' => true,
         'posts.user' => true,
         'posts.user.groups' => true,